<bookinfo>
<title>Linux DRM Developer's Guide</title>
+ <authorgroup>
+ <author>
+ <firstname>Jesse</firstname>
+ <surname>Barnes</surname>
+ <contrib>Initial version</contrib>
+ <affiliation>
+ <orgname>Intel Corporation</orgname>
+ <address>
+ <email>jesse.barnes@intel.com</email>
+ </address>
+ </affiliation>
+ </author>
+ <author>
+ <firstname>Laurent</firstname>
+ <surname>Pinchart</surname>
+ <contrib>Driver internals</contrib>
+ <affiliation>
+ <orgname>Ideas on board SPRL</orgname>
+ <address>
+ <email>laurent.pinchart@ideasonboard.com</email>
+ </address>
+ </affiliation>
+ </author>
+ </authorgroup>
+
<copyright>
<year>2008-2009</year>
- <holder>
- Intel Corporation (Jesse Barnes <jesse.barnes@intel.com>)
- </holder>
+ <year>2012</year>
+ <holder>Intel Corporation</holder>
+ <holder>Laurent Pinchart</holder>
</copyright>
<legalnotice>
the kernel source COPYING file.
</para>
</legalnotice>
+
+ <revhistory>
+ <!-- Put document revisions here, newest first. -->
+ <revision>
+ <revnumber>1.0</revnumber>
+ <date>2012-07-13</date>
+ <authorinitials>LP</authorinitials>
+ <revremark>Added extensive documentation about driver internals.
+ </revremark>
+ </revision>
+ </revhistory>
</bookinfo>
<toc></toc>
submission & fencing, suspend/resume support, and DMA
services.
</para>
- <para>
- The core of every DRM driver is struct drm_driver. Drivers
- typically statically initialize a drm_driver structure,
- then pass it to drm_init() at load time.
- </para>
<!-- Internals: driver init -->
<sect1>
- <title>Driver initialization</title>
- <para>
- Before calling the DRM initialization routines, the driver must
- first create and fill out a struct drm_driver structure.
- </para>
- <programlisting>
- static struct drm_driver driver = {
- /* Don't use MTRRs here; the Xserver or userspace app should
- * deal with them for Intel hardware.
- */
- .driver_features =
- DRIVER_USE_AGP | DRIVER_REQUIRE_AGP |
- DRIVER_HAVE_IRQ | DRIVER_IRQ_SHARED | DRIVER_MODESET,
- .load = i915_driver_load,
- .unload = i915_driver_unload,
- .firstopen = i915_driver_firstopen,
- .lastclose = i915_driver_lastclose,
- .preclose = i915_driver_preclose,
- .save = i915_save,
- .restore = i915_restore,
- .device_is_agp = i915_driver_device_is_agp,
- .get_vblank_counter = i915_get_vblank_counter,
- .enable_vblank = i915_enable_vblank,
- .disable_vblank = i915_disable_vblank,
- .irq_preinstall = i915_driver_irq_preinstall,
- .irq_postinstall = i915_driver_irq_postinstall,
- .irq_uninstall = i915_driver_irq_uninstall,
- .irq_handler = i915_driver_irq_handler,
- .reclaim_buffers = drm_core_reclaim_buffers,
- .get_map_ofs = drm_core_get_map_ofs,
- .get_reg_ofs = drm_core_get_reg_ofs,
- .fb_probe = intelfb_probe,
- .fb_remove = intelfb_remove,
- .fb_resize = intelfb_resize,
- .master_create = i915_master_create,
- .master_destroy = i915_master_destroy,
-#if defined(CONFIG_DEBUG_FS)
- .debugfs_init = i915_debugfs_init,
- .debugfs_cleanup = i915_debugfs_cleanup,
-#endif
- .gem_init_object = i915_gem_init_object,
- .gem_free_object = i915_gem_free_object,
- .gem_vm_ops = &i915_gem_vm_ops,
- .ioctls = i915_ioctls,
- .fops = {
- .owner = THIS_MODULE,
- .open = drm_open,
- .release = drm_release,
- .ioctl = drm_ioctl,
- .mmap = drm_mmap,
- .poll = drm_poll,
- .fasync = drm_fasync,
-#ifdef CONFIG_COMPAT
- .compat_ioctl = i915_compat_ioctl,
-#endif
- .llseek = noop_llseek,
- },
- .pci_driver = {
- .name = DRIVER_NAME,
- .id_table = pciidlist,
- .probe = probe,
- .remove = __devexit_p(drm_cleanup_pci),
- },
- .name = DRIVER_NAME,
- .desc = DRIVER_DESC,
- .date = DRIVER_DATE,
- .major = DRIVER_MAJOR,
- .minor = DRIVER_MINOR,
- .patchlevel = DRIVER_PATCHLEVEL,
- };
- </programlisting>
- <para>
- In the example above, taken from the i915 DRM driver, the driver
- sets several flags indicating what core features it supports;
- we go over the individual callbacks in later sections. Since
- flags indicate which features your driver supports to the DRM
- core, you need to set most of them prior to calling drm_init(). Some,
- like DRIVER_MODESET can be set later based on user supplied parameters,
- but that's the exception rather than the rule.
- </para>
- <variablelist>
- <title>Driver flags</title>
- <varlistentry>
- <term>DRIVER_USE_AGP</term>
- <listitem><para>
- Driver uses AGP interface
- </para></listitem>
- </varlistentry>
- <varlistentry>
- <term>DRIVER_REQUIRE_AGP</term>
- <listitem><para>
- Driver needs AGP interface to function.
- </para></listitem>
- </varlistentry>
- <varlistentry>
- <term>DRIVER_USE_MTRR</term>
- <listitem>
- <para>
- Driver uses MTRR interface for mapping memory. Deprecated.
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term>DRIVER_PCI_DMA</term>
- <listitem><para>
- Driver is capable of PCI DMA. Deprecated.
- </para></listitem>
- </varlistentry>
- <varlistentry>
- <term>DRIVER_SG</term>
- <listitem><para>
- Driver can perform scatter/gather DMA. Deprecated.
- </para></listitem>
- </varlistentry>
- <varlistentry>
- <term>DRIVER_HAVE_DMA</term>
- <listitem><para>Driver supports DMA. Deprecated.</para></listitem>
- </varlistentry>
- <varlistentry>
- <term>DRIVER_HAVE_IRQ</term><term>DRIVER_IRQ_SHARED</term>
- <listitem>
- <para>
- DRIVER_HAVE_IRQ indicates whether the driver has an IRQ
- handler. DRIVER_IRQ_SHARED indicates whether the device &
- handler support shared IRQs (note that this is required of
- PCI drivers).
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term>DRIVER_DMA_QUEUE</term>
- <listitem>
- <para>
- Should be set if the driver queues DMA requests and completes them
- asynchronously. Deprecated.
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term>DRIVER_FB_DMA</term>
- <listitem>
- <para>
- Driver supports DMA to/from the framebuffer. Deprecated.
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term>DRIVER_MODESET</term>
- <listitem>
- <para>
- Driver supports mode setting interfaces.
- </para>
- </listitem>
- </varlistentry>
- </variablelist>
- <para>
- In this specific case, the driver requires AGP and supports
- IRQs. DMA, as discussed later, is handled by device-specific ioctls
- in this case. It also supports the kernel mode setting APIs, though
- unlike in the actual i915 driver source, this example unconditionally
- exports KMS capability.
+ <title>Driver Initialization</title>
+ <para>
+ At the core of every DRM driver is a <structname>drm_driver</structname>
+ structure. Drivers typically statically initialize a drm_driver structure,
+ and then pass it to one of the <function>drm_*_init()</function> functions
+ to register it with the DRM subsystem.
</para>
- </sect1>
-
- <!-- Internals: driver load -->
-
- <sect1>
- <title>Driver load</title>
- <para>
- In the previous section, we saw what a typical drm_driver
- structure might look like. One of the more important fields in
- the structure is the hook for the load function.
- </para>
- <programlisting>
- static struct drm_driver driver = {
- ...
- .load = i915_driver_load,
- ...
- };
- </programlisting>
- <para>
- The load function has many responsibilities: allocating a driver
- private structure, specifying supported performance counters,
- configuring the device (e.g. mapping registers & command
- buffers), initializing the memory manager, and setting up the
- initial output configuration.
- </para>
- <para>
- If compatibility is a concern (e.g. with drivers converted over
- to the new interfaces from the old ones), care must be taken to
- prevent device initialization and control that is incompatible with
- currently active userspace drivers. For instance, if user
- level mode setting drivers are in use, it would be problematic
- to perform output discovery & configuration at load time.
- Likewise, if user-level drivers unaware of memory management are
- in use, memory management and command buffer setup may need to
- be omitted. These requirements are driver-specific, and care
- needs to be taken to keep both old and new applications and
- libraries working. The i915 driver supports the "modeset"
- module parameter to control whether advanced features are
- enabled at load time or in legacy fashion.
+ <para>
+ The <structname>drm_driver</structname> structure contains static
+ information that describes the driver and features it supports, and
+ pointers to methods that the DRM core will call to implement the DRM API.
+ We will first go through the <structname>drm_driver</structname> static
+ information fields, and will then describe individual operations in
+ details as they get used in later sections.
</para>
-
<sect2>
- <title>Driver private & performance counters</title>
- <para>
- The driver private hangs off the main drm_device structure and
- can be used for tracking various device-specific bits of
- information, like register offsets, command buffer status,
- register state for suspend/resume, etc. At load time, a
- driver may simply allocate one and set drm_device.dev_priv
- appropriately; it should be freed and drm_device.dev_priv set
- to NULL when the driver is unloaded.
- </para>
+ <title>Driver Information</title>
+ <sect3>
+ <title>Driver Features</title>
+ <para>
+ Drivers inform the DRM core about their requirements and supported
+ features by setting appropriate flags in the
+ <structfield>driver_features</structfield> field. Since those flags
+ influence the DRM core behaviour since registration time, most of them
+ must be set to registering the <structname>drm_driver</structname>
+ instance.
+ </para>
+ <synopsis>u32 driver_features;</synopsis>
+ <variablelist>
+ <title>Driver Feature Flags</title>
+ <varlistentry>
+ <term>DRIVER_USE_AGP</term>
+ <listitem><para>
+ Driver uses AGP interface, the DRM core will manage AGP resources.
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRIVER_REQUIRE_AGP</term>
+ <listitem><para>
+ Driver needs AGP interface to function. AGP initialization failure
+ will become a fatal error.
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRIVER_USE_MTRR</term>
+ <listitem><para>
+ Driver uses MTRR interface for mapping memory, the DRM core will
+ manage MTRR resources. Deprecated.
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRIVER_PCI_DMA</term>
+ <listitem><para>
+ Driver is capable of PCI DMA, mapping of PCI DMA buffers to
+ userspace will be enabled. Deprecated.
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRIVER_SG</term>
+ <listitem><para>
+ Driver can perform scatter/gather DMA, allocation and mapping of
+ scatter/gather buffers will be enabled. Deprecated.
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRIVER_HAVE_DMA</term>
+ <listitem><para>
+ Driver supports DMA, the userspace DMA API will be supported.
+ Deprecated.
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRIVER_HAVE_IRQ</term><term>DRIVER_IRQ_SHARED</term>
+ <listitem><para>
+ DRIVER_HAVE_IRQ indicates whether the driver has an IRQ handler. The
+ DRM core will automatically register an interrupt handler when the
+ flag is set. DRIVER_IRQ_SHARED indicates whether the device &
+ handler support shared IRQs (note that this is required of PCI
+ drivers).
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRIVER_IRQ_VBL</term>
+ <listitem><para>Unused. Deprecated.</para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRIVER_DMA_QUEUE</term>
+ <listitem><para>
+ Should be set if the driver queues DMA requests and completes them
+ asynchronously. Deprecated.
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRIVER_FB_DMA</term>
+ <listitem><para>
+ Driver supports DMA to/from the framebuffer, mapping of frambuffer
+ DMA buffers to userspace will be supported. Deprecated.
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRIVER_IRQ_VBL2</term>
+ <listitem><para>Unused. Deprecated.</para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRIVER_GEM</term>
+ <listitem><para>
+ Driver use the GEM memory manager.
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRIVER_MODESET</term>
+ <listitem><para>
+ Driver supports mode setting interfaces (KMS).
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRIVER_PRIME</term>
+ <listitem><para>
+ Driver implements DRM PRIME buffer sharing.
+ </para></listitem>
+ </varlistentry>
+ </variablelist>
+ </sect3>
+ <sect3>
+ <title>Major, Minor and Patchlevel</title>
+ <synopsis>int major;
+int minor;
+int patchlevel;</synopsis>
+ <para>
+ The DRM core identifies driver versions by a major, minor and patch
+ level triplet. The information is printed to the kernel log at
+ initialization time and passed to userspace through the
+ DRM_IOCTL_VERSION ioctl.
+ </para>
+ <para>
+ The major and minor numbers are also used to verify the requested driver
+ API version passed to DRM_IOCTL_SET_VERSION. When the driver API changes
+ between minor versions, applications can call DRM_IOCTL_SET_VERSION to
+ select a specific version of the API. If the requested major isn't equal
+ to the driver major, or the requested minor is larger than the driver
+ minor, the DRM_IOCTL_SET_VERSION call will return an error. Otherwise
+ the driver's set_version() method will be called with the requested
+ version.
+ </para>
+ </sect3>
+ <sect3>
+ <title>Name, Description and Date</title>
+ <synopsis>char *name;
+char *desc;
+char *date;</synopsis>
+ <para>
+ The driver name is printed to the kernel log at initialization time,
+ used for IRQ registration and passed to userspace through
+ DRM_IOCTL_VERSION.
+ </para>
+ <para>
+ The driver description is a purely informative string passed to
+ userspace through the DRM_IOCTL_VERSION ioctl and otherwise unused by
+ the kernel.
+ </para>
+ <para>
+ The driver date, formatted as YYYYMMDD, is meant to identify the date of
+ the latest modification to the driver. However, as most drivers fail to
+ update it, its value is mostly useless. The DRM core prints it to the
+ kernel log at initialization time and passes it to userspace through the
+ DRM_IOCTL_VERSION ioctl.
+ </para>
+ </sect3>
+ </sect2>
+ <sect2>
+ <title>Driver Load</title>
<para>
- The DRM supports several counters which may be used for rough
- performance characterization. Note that the DRM stat counter
- system is not often used by applications, and supporting
- additional counters is completely optional.
+ The <methodname>load</methodname> method is the driver and device
+ initialization entry point. The method is responsible for allocating and
+ initializing driver private data, specifying supported performance
+ counters, performing resource allocation and mapping (e.g. acquiring
+ clocks, mapping registers or allocating command buffers), initializing
+ the memory manager (<xref linkend="drm-memory-management"/>), installing
+ the IRQ handler (<xref linkend="drm-irq-registration"/>), setting up
+ vertical blanking handling (<xref linkend="drm-vertical-blank"/>), mode
+ setting (<xref linkend="drm-mode-setting"/>) and initial output
+ configuration (<xref linkend="drm-kms-init"/>).
</para>
+ <note><para>
+ If compatibility is a concern (e.g. with drivers converted over from
+ User Mode Setting to Kernel Mode Setting), care must be taken to prevent
+ device initialization and control that is incompatible with currently
+ active userspace drivers. For instance, if user level mode setting
+ drivers are in use, it would be problematic to perform output discovery
+ & configuration at load time. Likewise, if user-level drivers
+ unaware of memory management are in use, memory management and command
+ buffer setup may need to be omitted. These requirements are
+ driver-specific, and care needs to be taken to keep both old and new
+ applications and libraries working.
+ </para></note>
+ <synopsis>int (*load) (struct drm_device *, unsigned long flags);</synopsis>
<para>
- These interfaces are deprecated and should not be used. If performance
- monitoring is desired, the developer should investigate and
- potentially enhance the kernel perf and tracing infrastructure to export
- GPU related performance information for consumption by performance
- monitoring tools and applications.
+ The method takes two arguments, a pointer to the newly created
+ <structname>drm_device</structname> and flags. The flags are used to
+ pass the <structfield>driver_data</structfield> field of the device id
+ corresponding to the device passed to <function>drm_*_init()</function>.
+ Only PCI devices currently use this, USB and platform DRM drivers have
+ their <methodname>load</methodname> method called with flags to 0.
</para>
+ <sect3>
+ <title>Driver Private & Performance Counters</title>
+ <para>
+ The driver private hangs off the main
+ <structname>drm_device</structname> structure and can be used for
+ tracking various device-specific bits of information, like register
+ offsets, command buffer status, register state for suspend/resume, etc.
+ At load time, a driver may simply allocate one and set
+ <structname>drm_device</structname>.<structfield>dev_priv</structfield>
+ appropriately; it should be freed and
+ <structname>drm_device</structname>.<structfield>dev_priv</structfield>
+ set to NULL when the driver is unloaded.
+ </para>
+ <para>
+ DRM supports several counters which were used for rough performance
+ characterization. This stat counter system is deprecated and should not
+ be used. If performance monitoring is desired, the developer should
+ investigate and potentially enhance the kernel perf and tracing
+ infrastructure to export GPU related performance information for
+ consumption by performance monitoring tools and applications.
+ </para>
+ </sect3>
+ <sect3 id="drm-irq-registration">
+ <title>IRQ Registration</title>
+ <para>
+ The DRM core tries to facilitate IRQ handler registration and
+ unregistration by providing <function>drm_irq_install</function> and
+ <function>drm_irq_uninstall</function> functions. Those functions only
+ support a single interrupt per device.
+ </para>
+ <!--!Fdrivers/char/drm/drm_irq.c drm_irq_install-->
+ <para>
+ Both functions get the device IRQ by calling
+ <function>drm_dev_to_irq</function>. This inline function will call a
+ bus-specific operation to retrieve the IRQ number. For platform devices,
+ <function>platform_get_irq</function>(..., 0) is used to retrieve the
+ IRQ number.
+ </para>
+ <para>
+ <function>drm_irq_install</function> starts by calling the
+ <methodname>irq_preinstall</methodname> driver operation. The operation
+ is optional and must make sure that the interrupt will not get fired by
+ clearing all pending interrupt flags or disabling the interrupt.
+ </para>
+ <para>
+ The IRQ will then be requested by a call to
+ <function>request_irq</function>. If the DRIVER_IRQ_SHARED driver
+ feature flag is set, a shared (IRQF_SHARED) IRQ handler will be
+ requested.
+ </para>
+ <para>
+ The IRQ handler function must be provided as the mandatory irq_handler
+ driver operation. It will get passed directly to
+ <function>request_irq</function> and thus has the same prototype as all
+ IRQ handlers. It will get called with a pointer to the DRM device as the
+ second argument.
+ </para>
+ <para>
+ Finally the function calls the optional
+ <methodname>irq_postinstall</methodname> driver operation. The operation
+ usually enables interrupts (excluding the vblank interrupt, which is
+ enabled separately), but drivers may choose to enable/disable interrupts
+ at a different time.
+ </para>
+ <para>
+ <function>drm_irq_uninstall</function> is similarly used to uninstall an
+ IRQ handler. It starts by waking up all processes waiting on a vblank
+ interrupt to make sure they don't hang, and then calls the optional
+ <methodname>irq_uninstall</methodname> driver operation. The operation
+ must disable all hardware interrupts. Finally the function frees the IRQ
+ by calling <function>free_irq</function>.
+ </para>
+ </sect3>
+ <sect3>
+ <title>Memory Manager Initialization</title>
+ <para>
+ Every DRM driver requires a memory manager which must be initialized at
+ load time. DRM currently contains two memory managers, the Translation
+ Table Manager (TTM) and the Graphics Execution Manager (GEM).
+ This document describes the use of the GEM memory manager only. See
+ <xref linkend="drm-memory-management"/> for details.
+ </para>
+ </sect3>
+ <sect3>
+ <title>Miscellaneous Device Configuration</title>
+ <para>
+ Another task that may be necessary for PCI devices during configuration
+ is mapping the video BIOS. On many devices, the VBIOS describes device
+ configuration, LCD panel timings (if any), and contains flags indicating
+ device state. Mapping the BIOS can be done using the pci_map_rom() call,
+ a convenience function that takes care of mapping the actual ROM,
+ whether it has been shadowed into memory (typically at address 0xc0000)
+ or exists on the PCI device in the ROM BAR. Note that after the ROM has
+ been mapped and any necessary information has been extracted, it should
+ be unmapped; on many devices, the ROM address decoder is shared with
+ other BARs, so leaving it mapped could cause undesired behaviour like
+ hangs or memory corruption.
+ <!--!Fdrivers/pci/rom.c pci_map_rom-->
+ </para>
+ </sect3>
</sect2>
+ </sect1>
- <sect2>
- <title>Configuring the device</title>
- <para>
- Obviously, device configuration is device-specific.
- However, there are several common operations: finding a
- device's PCI resources, mapping them, and potentially setting
- up an IRQ handler.
- </para>
- <para>
- Finding & mapping resources is fairly straightforward. The
- DRM wrapper functions, drm_get_resource_start() and
- drm_get_resource_len(), may be used to find BARs on the given
- drm_device struct. Once those values have been retrieved, the
- driver load function can call drm_addmap() to create a new
- mapping for the BAR in question. Note that you probably want a
- drm_local_map_t in your driver private structure to track any
- mappings you create.
-<!-- !Fdrivers/gpu/drm/drm_bufs.c drm_get_resource_* -->
-<!-- !Finclude/drm/drmP.h drm_local_map_t -->
- </para>
- <para>
- if compatibility with other operating systems isn't a concern
- (DRM drivers can run under various BSD variants and OpenSolaris),
- native Linux calls may be used for the above, e.g. pci_resource_*
- and iomap*/iounmap. See the Linux device driver book for more
- info.
- </para>
- <para>
- Once you have a register map, you may use the DRM_READn() and
- DRM_WRITEn() macros to access the registers on your device, or
- use driver-specific versions to offset into your MMIO space
- relative to a driver-specific base pointer (see I915_READ for
- an example).
- </para>
- <para>
- If your device supports interrupt generation, you may want to
- set up an interrupt handler when the driver is loaded. This
- is done using the drm_irq_install() function. If your device
- supports vertical blank interrupts, it should call
- drm_vblank_init() to initialize the core vblank handling code before
- enabling interrupts on your device. This ensures the vblank related
- structures are allocated and allows the core to handle vblank events.
- </para>
-<!--!Fdrivers/char/drm/drm_irq.c drm_irq_install-->
- <para>
- Once your interrupt handler is registered (it uses your
- drm_driver.irq_handler as the actual interrupt handling
- function), you can safely enable interrupts on your device,
- assuming any other state your interrupt handler uses is also
- initialized.
- </para>
- <para>
- Another task that may be necessary during configuration is
- mapping the video BIOS. On many devices, the VBIOS describes
- device configuration, LCD panel timings (if any), and contains
- flags indicating device state. Mapping the BIOS can be done
- using the pci_map_rom() call, a convenience function that
- takes care of mapping the actual ROM, whether it has been
- shadowed into memory (typically at address 0xc0000) or exists
- on the PCI device in the ROM BAR. Note that after the ROM
- has been mapped and any necessary information has been extracted,
- it should be unmapped; on many devices, the ROM address decoder is
- shared with other BARs, so leaving it mapped could cause
- undesired behavior like hangs or memory corruption.
-<!--!Fdrivers/pci/rom.c pci_map_rom-->
- </para>
- </sect2>
+ <!-- Internals: memory management -->
+ <sect1 id="drm-memory-management">
+ <title>Memory management</title>
+ <para>
+ Modern Linux systems require large amount of graphics memory to store
+ frame buffers, textures, vertices and other graphics-related data. Given
+ the very dynamic nature of many of that data, managing graphics memory
+ efficiently is thus crucial for the graphics stack and plays a central
+ role in the DRM infrastructure.
+ </para>
+ <para>
+ The DRM core includes two memory managers, namely Translation Table Maps
+ (TTM) and Graphics Execution Manager (GEM). TTM was the first DRM memory
+ manager to be developed and tried to be a one-size-fits-them all
+ solution. It provides a single userspace API to accomodate the need of
+ all hardware, supporting both Unified Memory Architecture (UMA) devices
+ and devices with dedicated video RAM (i.e. most discrete video cards).
+ This resulted in a large, complex piece of code that turned out to be
+ hard to use for driver development.
+ </para>
+ <para>
+ GEM started as an Intel-sponsored project in reaction to TTM's
+ complexity. Its design philosophy is completely different: instead of
+ providing a solution to every graphics memory-related problems, GEM
+ identified common code between drivers and created a support library to
+ share it. GEM has simpler initialization and execution requirements than
+ TTM, but has no video RAM management capabitilies and is thus limited to
+ UMA devices.
+ </para>
<sect2>
- <title>Memory manager initialization</title>
- <para>
- In order to allocate command buffers, cursor memory, scanout
- buffers, etc., as well as support the latest features provided
- by packages like Mesa and the X.Org X server, your driver
- should support a memory manager.
- </para>
+ <title>The Translation Table Manager (TTM)</title>
<para>
- If your driver supports memory management (it should!), you
- need to set that up at load time as well. How you initialize
- it depends on which memory manager you're using: TTM or GEM.
+ TTM design background and information belongs here.
</para>
<sect3>
<title>TTM initialization</title>
- <para>
- TTM (for Translation Table Manager) manages video memory and
- aperture space for graphics devices. TTM supports both UMA devices
- and devices with dedicated video RAM (VRAM), i.e. most discrete
- graphics devices. If your device has dedicated RAM, supporting
- TTM is desirable. TTM also integrates tightly with your
- driver-specific buffer execution function. See the radeon
- driver for examples.
- </para>
- <para>
- The core TTM structure is the ttm_bo_driver struct. It contains
- several fields with function pointers for initializing the TTM,
- allocating and freeing memory, waiting for command completion
- and fence synchronization, and memory migration. See the
- radeon_ttm.c file for an example of usage.
+ <warning><para>This section is outdated.</para></warning>
+ <para>
+ Drivers wishing to support TTM must fill out a drm_bo_driver
+ structure. The structure contains several fields with function
+ pointers for initializing the TTM, allocating and freeing memory,
+ waiting for command completion and fence synchronization, and memory
+ migration. See the radeon_ttm.c file for an example of usage.
</para>
<para>
The ttm_global_reference structure is made up of several fields:
count for the TTM, which will call your initialization function.
</para>
</sect3>
+ </sect2>
+ <sect2 id="drm-gem">
+ <title>The Graphics Execution Manager (GEM)</title>
+ <para>
+ The GEM design approach has resulted in a memory manager that doesn't
+ provide full coverage of all (or even all common) use cases in its
+ userspace or kernel API. GEM exposes a set of standard memory-related
+ operations to userspace and a set of helper functions to drivers, and let
+ drivers implement hardware-specific operations with their own private API.
+ </para>
+ <para>
+ The GEM userspace API is described in the
+ <ulink url="http://lwn.net/Articles/283798/"><citetitle>GEM - the Graphics
+ Execution Manager</citetitle></ulink> article on LWN. While slightly
+ outdated, the document provides a good overview of the GEM API principles.
+ Buffer allocation and read and write operations, described as part of the
+ common GEM API, are currently implemented using driver-specific ioctls.
+ </para>
+ <para>
+ GEM is data-agnostic. It manages abstract buffer objects without knowing
+ what individual buffers contain. APIs that require knowledge of buffer
+ contents or purpose, such as buffer allocation or synchronization
+ primitives, are thus outside of the scope of GEM and must be implemented
+ using driver-specific ioctls.
+ </para>
+ <para>
+ On a fundamental level, GEM involves several operations:
+ <itemizedlist>
+ <listitem>Memory allocation and freeing</listitem>
+ <listitem>Command execution</listitem>
+ <listitem>Aperture management at command execution time</listitem>
+ </itemizedlist>
+ Buffer object allocation is relatively straightforward and largely
+ provided by Linux's shmem layer, which provides memory to back each
+ object.
+ </para>
+ <para>
+ Device-specific operations, such as command execution, pinning, buffer
+ read & write, mapping, and domain ownership transfers are left to
+ driver-specific ioctls.
+ </para>
+ <sect3>
+ <title>GEM Initialization</title>
+ <para>
+ Drivers that use GEM must set the DRIVER_GEM bit in the struct
+ <structname>drm_driver</structname>
+ <structfield>driver_features</structfield> field. The DRM core will
+ then automatically initialize the GEM core before calling the
+ <methodname>load</methodname> operation. Behind the scene, this will
+ create a DRM Memory Manager object which provides an address space
+ pool for object allocation.
+ </para>
+ <para>
+ In a KMS configuration, drivers need to allocate and initialize a
+ command ring buffer following core GEM initialization if required by
+ the hardware. UMA devices usually have what is called a "stolen"
+ memory region, which provides space for the initial framebuffer and
+ large, contiguous memory regions required by the device. This space is
+ typically not managed by GEM, and must be initialized separately into
+ its own DRM MM object.
+ </para>
+ </sect3>
<sect3>
- <title>GEM initialization</title>
- <para>
- GEM is an alternative to TTM, designed specifically for UMA
- devices. It has simpler initialization and execution requirements
- than TTM, but has no VRAM management capability. Core GEM
- is initialized by calling drm_mm_init() to create
- a GTT DRM MM object, which provides an address space pool for
- object allocation. In a KMS configuration, the driver
- needs to allocate and initialize a command ring buffer following
- core GEM initialization. A UMA device usually has what is called a
- "stolen" memory region, which provides space for the initial
- framebuffer and large, contiguous memory regions required by the
- device. This space is not typically managed by GEM, and it must
- be initialized separately into its own DRM MM object.
- </para>
- <para>
- Initialization is driver-specific. In the case of Intel
- integrated graphics chips like 965GM, GEM initialization can
- be done by calling the internal GEM init function,
- i915_gem_do_init(). Since the 965GM is a UMA device
- (i.e. it doesn't have dedicated VRAM), GEM manages
- making regular RAM available for GPU operations. Memory set
- aside by the BIOS (called "stolen" memory by the i915
- driver) is managed by the DRM memrange allocator; the
- rest of the aperture is managed by GEM.
- <programlisting>
- /* Basic memrange allocator for stolen space (aka vram) */
- drm_memrange_init(&dev_priv->vram, 0, prealloc_size);
- /* Let GEM Manage from end of prealloc space to end of aperture */
- i915_gem_do_init(dev, prealloc_size, agp_size);
- </programlisting>
-<!--!Edrivers/char/drm/drm_memrange.c-->
- </para>
- <para>
- Once the memory manager has been set up, we may allocate the
- command buffer. In the i915 case, this is also done with a
- GEM function, i915_gem_init_ringbuffer().
- </para>
+ <title>GEM Objects Creation</title>
+ <para>
+ GEM splits creation of GEM objects and allocation of the memory that
+ backs them in two distinct operations.
+ </para>
+ <para>
+ GEM objects are represented by an instance of struct
+ <structname>drm_gem_object</structname>. Drivers usually need to extend
+ GEM objects with private information and thus create a driver-specific
+ GEM object structure type that embeds an instance of struct
+ <structname>drm_gem_object</structname>.
+ </para>
+ <para>
+ To create a GEM object, a driver allocates memory for an instance of its
+ specific GEM object type and initializes the embedded struct
+ <structname>drm_gem_object</structname> with a call to
+ <function>drm_gem_object_init</function>. The function takes a pointer to
+ the DRM device, a pointer to the GEM object and the buffer object size
+ in bytes.
+ </para>
+ <para>
+ GEM uses shmem to allocate anonymous pageable memory.
+ <function>drm_gem_object_init</function> will create an shmfs file of
+ the requested size and store it into the struct
+ <structname>drm_gem_object</structname> <structfield>filp</structfield>
+ field. The memory is used as either main storage for the object when the
+ graphics hardware uses system memory directly or as a backing store
+ otherwise.
+ </para>
+ <para>
+ Drivers are responsible for the actual physical pages allocation by
+ calling <function>shmem_read_mapping_page_gfp</function> for each page.
+ Note that they can decide to allocate pages when initializing the GEM
+ object, or to delay allocation until the memory is needed (for instance
+ when a page fault occurs as a result of a userspace memory access or
+ when the driver needs to start a DMA transfer involving the memory).
+ </para>
+ <para>
+ Anonymous pageable memory allocation is not always desired, for instance
+ when the hardware requires physically contiguous system memory as is
+ often the case in embedded devices. Drivers can create GEM objects with
+ no shmfs backing (called private GEM objects) by initializing them with
+ a call to <function>drm_gem_private_object_init</function> instead of
+ <function>drm_gem_object_init</function>. Storage for private GEM
+ objects must be managed by drivers.
+ </para>
+ <para>
+ Drivers that do not need to extend GEM objects with private information
+ can call the <function>drm_gem_object_alloc</function> function to
+ allocate and initialize a struct <structname>drm_gem_object</structname>
+ instance. The GEM core will call the optional driver
+ <methodname>gem_init_object</methodname> operation after initializing
+ the GEM object with <function>drm_gem_object_init</function>.
+ <synopsis>int (*gem_init_object) (struct drm_gem_object *obj);</synopsis>
+ </para>
+ <para>
+ No alloc-and-init function exists for private GEM objects.
+ </para>
+ </sect3>
+ <sect3>
+ <title>GEM Objects Lifetime</title>
+ <para>
+ All GEM objects are reference-counted by the GEM core. References can be
+ acquired and release by <function>calling drm_gem_object_reference</function>
+ and <function>drm_gem_object_unreference</function> respectively. The
+ caller must hold the <structname>drm_device</structname>
+ <structfield>struct_mutex</structfield> lock. As a convenience, GEM
+ provides the <function>drm_gem_object_reference_unlocked</function> and
+ <function>drm_gem_object_unreference_unlocked</function> functions that
+ can be called without holding the lock.
+ </para>
+ <para>
+ When the last reference to a GEM object is released the GEM core calls
+ the <structname>drm_driver</structname>
+ <methodname>gem_free_object</methodname> operation. That operation is
+ mandatory for GEM-enabled drivers and must free the GEM object and all
+ associated resources.
+ </para>
+ <para>
+ <synopsis>void (*gem_free_object) (struct drm_gem_object *obj);</synopsis>
+ Drivers are responsible for freeing all GEM object resources, including
+ the resources created by the GEM core. If an mmap offset has been
+ created for the object (in which case
+ <structname>drm_gem_object</structname>::<structfield>map_list</structfield>::<structfield>map</structfield>
+ is not NULL) it must be freed by a call to
+ <function>drm_gem_free_mmap_offset</function>. The shmfs backing store
+ must be released by calling <function>drm_gem_object_release</function>
+ (that function can safely be called if no shmfs backing store has been
+ created).
+ </para>
+ </sect3>
+ <sect3>
+ <title>GEM Objects Naming</title>
+ <para>
+ Communication between userspace and the kernel refers to GEM objects
+ using local handles, global names or, more recently, file descriptors.
+ All of those are 32-bit integer values; the usual Linux kernel limits
+ apply to the file descriptors.
+ </para>
+ <para>
+ GEM handles are local to a DRM file. Applications get a handle to a GEM
+ object through a driver-specific ioctl, and can use that handle to refer
+ to the GEM object in other standard or driver-specific ioctls. Closing a
+ DRM file handle frees all its GEM handles and dereferences the
+ associated GEM objects.
+ </para>
+ <para>
+ To create a handle for a GEM object drivers call
+ <function>drm_gem_handle_create</function>. The function takes a pointer
+ to the DRM file and the GEM object and returns a locally unique handle.
+ When the handle is no longer needed drivers delete it with a call to
+ <function>drm_gem_handle_delete</function>. Finally the GEM object
+ associated with a handle can be retrieved by a call to
+ <function>drm_gem_object_lookup</function>.
+ </para>
+ <para>
+ Handles don't take ownership of GEM objects, they only take a reference
+ to the object that will be dropped when the handle is destroyed. To
+ avoid leaking GEM objects, drivers must make sure they drop the
+ reference(s) they own (such as the initial reference taken at object
+ creation time) as appropriate, without any special consideration for the
+ handle. For example, in the particular case of combined GEM object and
+ handle creation in the implementation of the
+ <methodname>dumb_create</methodname> operation, drivers must drop the
+ initial reference to the GEM object before returning the handle.
+ </para>
+ <para>
+ GEM names are similar in purpose to handles but are not local to DRM
+ files. They can be passed between processes to reference a GEM object
+ globally. Names can't be used directly to refer to objects in the DRM
+ API, applications must convert handles to names and names to handles
+ using the DRM_IOCTL_GEM_FLINK and DRM_IOCTL_GEM_OPEN ioctls
+ respectively. The conversion is handled by the DRM core without any
+ driver-specific support.
+ </para>
+ <para>
+ Similar to global names, GEM file descriptors are also used to share GEM
+ objects across processes. They offer additional security: as file
+ descriptors must be explictly sent over UNIX domain sockets to be shared
+ between applications, they can't be guessed like the globally unique GEM
+ names.
+ </para>
+ <para>
+ Drivers that support GEM file descriptors, also known as the DRM PRIME
+ API, must set the DRIVER_PRIME bit in the struct
+ <structname>drm_driver</structname>
+ <structfield>driver_features</structfield> field, and implement the
+ <methodname>prime_handle_to_fd</methodname> and
+ <methodname>prime_fd_to_handle</methodname> operations.
+ </para>
+ <para>
+ <synopsis>int (*prime_handle_to_fd)(struct drm_device *dev,
+ struct drm_file *file_priv, uint32_t handle,
+ uint32_t flags, int *prime_fd);
+ int (*prime_fd_to_handle)(struct drm_device *dev,
+ struct drm_file *file_priv, int prime_fd,
+ uint32_t *handle);</synopsis>
+ Those two operations convert a handle to a PRIME file descriptor and
+ vice versa. Drivers must use the kernel dma-buf buffer sharing framework
+ to manage the PRIME file descriptors.
+ </para>
+ <para>
+ While non-GEM drivers must implement the operations themselves, GEM
+ drivers must use the <function>drm_gem_prime_handle_to_fd</function>
+ and <function>drm_gem_prime_fd_to_handle</function> helper functions.
+ Those helpers rely on the driver
+ <methodname>gem_prime_export</methodname> and
+ <methodname>gem_prime_import</methodname> operations to create a dma-buf
+ instance from a GEM object (dma-buf exporter role) and to create a GEM
+ object from a dma-buf instance (dma-buf importer role).
+ </para>
+ <para>
+ <synopsis>struct dma_buf * (*gem_prime_export)(struct drm_device *dev,
+ struct drm_gem_object *obj,
+ int flags);
+ struct drm_gem_object * (*gem_prime_import)(struct drm_device *dev,
+ struct dma_buf *dma_buf);</synopsis>
+ These two operations are mandatory for GEM drivers that support DRM
+ PRIME.
+ </para>
+ </sect3>
+ <sect3 id="drm-gem-objects-mapping">
+ <title>GEM Objects Mapping</title>
+ <para>
+ Because mapping operations are fairly heavyweight GEM favours
+ read/write-like access to buffers, implemented through driver-specific
+ ioctls, over mapping buffers to userspace. However, when random access
+ to the buffer is needed (to perform software rendering for instance),
+ direct access to the object can be more efficient.
+ </para>
+ <para>
+ The mmap system call can't be used directly to map GEM objects, as they
+ don't have their own file handle. Two alternative methods currently
+ co-exist to map GEM objects to userspace. The first method uses a
+ driver-specific ioctl to perform the mapping operation, calling
+ <function>do_mmap</function> under the hood. This is often considered
+ dubious, seems to be discouraged for new GEM-enabled drivers, and will
+ thus not be described here.
+ </para>
+ <para>
+ The second method uses the mmap system call on the DRM file handle.
+ <synopsis>void *mmap(void *addr, size_t length, int prot, int flags, int fd,
+ off_t offset);</synopsis>
+ DRM identifies the GEM object to be mapped by a fake offset passed
+ through the mmap offset argument. Prior to being mapped, a GEM object
+ must thus be associated with a fake offset. To do so, drivers must call
+ <function>drm_gem_create_mmap_offset</function> on the object. The
+ function allocates a fake offset range from a pool and stores the
+ offset divided by PAGE_SIZE in
+ <literal>obj->map_list.hash.key</literal>. Care must be taken not to
+ call <function>drm_gem_create_mmap_offset</function> if a fake offset
+ has already been allocated for the object. This can be tested by
+ <literal>obj->map_list.map</literal> being non-NULL.
+ </para>
+ <para>
+ Once allocated, the fake offset value
+ (<literal>obj->map_list.hash.key << PAGE_SHIFT</literal>)
+ must be passed to the application in a driver-specific way and can then
+ be used as the mmap offset argument.
+ </para>
+ <para>
+ The GEM core provides a helper method <function>drm_gem_mmap</function>
+ to handle object mapping. The method can be set directly as the mmap
+ file operation handler. It will look up the GEM object based on the
+ offset value and set the VMA operations to the
+ <structname>drm_driver</structname> <structfield>gem_vm_ops</structfield>
+ field. Note that <function>drm_gem_mmap</function> doesn't map memory to
+ userspace, but relies on the driver-provided fault handler to map pages
+ individually.
+ </para>
+ <para>
+ To use <function>drm_gem_mmap</function>, drivers must fill the struct
+ <structname>drm_driver</structname> <structfield>gem_vm_ops</structfield>
+ field with a pointer to VM operations.
+ </para>
+ <para>
+ <synopsis>struct vm_operations_struct *gem_vm_ops
+
+ struct vm_operations_struct {
+ void (*open)(struct vm_area_struct * area);
+ void (*close)(struct vm_area_struct * area);
+ int (*fault)(struct vm_area_struct *vma, struct vm_fault *vmf);
+ };</synopsis>
+ </para>
+ <para>
+ The <methodname>open</methodname> and <methodname>close</methodname>
+ operations must update the GEM object reference count. Drivers can use
+ the <function>drm_gem_vm_open</function> and
+ <function>drm_gem_vm_close</function> helper functions directly as open
+ and close handlers.
+ </para>
+ <para>
+ The fault operation handler is responsible for mapping individual pages
+ to userspace when a page fault occurs. Depending on the memory
+ allocation scheme, drivers can allocate pages at fault time, or can
+ decide to allocate memory for the GEM object at the time the object is
+ created.
+ </para>
+ <para>
+ Drivers that want to map the GEM object upfront instead of handling page
+ faults can implement their own mmap file operation handler.
+ </para>
+ </sect3>
+ <sect3>
+ <title>Dumb GEM Objects</title>
+ <para>
+ The GEM API doesn't standardize GEM objects creation and leaves it to
+ driver-specific ioctls. While not an issue for full-fledged graphics
+ stacks that include device-specific userspace components (in libdrm for
+ instance), this limit makes DRM-based early boot graphics unnecessarily
+ complex.
+ </para>
+ <para>
+ Dumb GEM objects partly alleviate the problem by providing a standard
+ API to create dumb buffers suitable for scanout, which can then be used
+ to create KMS frame buffers.
+ </para>
+ <para>
+ To support dumb GEM objects drivers must implement the
+ <methodname>dumb_create</methodname>,
+ <methodname>dumb_destroy</methodname> and
+ <methodname>dumb_map_offset</methodname> operations.
+ </para>
+ <itemizedlist>
+ <listitem>
+ <synopsis>int (*dumb_create)(struct drm_file *file_priv, struct drm_device *dev,
+ struct drm_mode_create_dumb *args);</synopsis>
+ <para>
+ The <methodname>dumb_create</methodname> operation creates a GEM
+ object suitable for scanout based on the width, height and depth
+ from the struct <structname>drm_mode_create_dumb</structname>
+ argument. It fills the argument's <structfield>handle</structfield>,
+ <structfield>pitch</structfield> and <structfield>size</structfield>
+ fields with a handle for the newly created GEM object and its line
+ pitch and size in bytes.
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>int (*dumb_destroy)(struct drm_file *file_priv, struct drm_device *dev,
+ uint32_t handle);</synopsis>
+ <para>
+ The <methodname>dumb_destroy</methodname> operation destroys a dumb
+ GEM object created by <methodname>dumb_create</methodname>.
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>int (*dumb_map_offset)(struct drm_file *file_priv, struct drm_device *dev,
+ uint32_t handle, uint64_t *offset);</synopsis>
+ <para>
+ The <methodname>dumb_map_offset</methodname> operation associates an
+ mmap fake offset with the GEM object given by the handle and returns
+ it. Drivers must use the
+ <function>drm_gem_create_mmap_offset</function> function to
+ associate the fake offset as described in
+ <xref linkend="drm-gem-objects-mapping"/>.
+ </para>
+ </listitem>
+ </itemizedlist>
+ </sect3>
+ <sect3>
+ <title>Memory Coherency</title>
+ <para>
+ When mapped to the device or used in a command buffer, backing pages
+ for an object are flushed to memory and marked write combined so as to
+ be coherent with the GPU. Likewise, if the CPU accesses an object
+ after the GPU has finished rendering to the object, then the object
+ must be made coherent with the CPU's view of memory, usually involving
+ GPU cache flushing of various kinds. This core CPU<->GPU
+ coherency management is provided by a device-specific ioctl, which
+ evaluates an object's current domain and performs any necessary
+ flushing or synchronization to put the object into the desired
+ coherency domain (note that the object may be busy, i.e. an active
+ render target; in that case, setting the domain blocks the client and
+ waits for rendering to complete before performing any necessary
+ flushing operations).
+ </para>
+ </sect3>
+ <sect3>
+ <title>Command Execution</title>
+ <para>
+ Perhaps the most important GEM function for GPU devices is providing a
+ command execution interface to clients. Client programs construct
+ command buffers containing references to previously allocated memory
+ objects, and then submit them to GEM. At that point, GEM takes care to
+ bind all the objects into the GTT, execute the buffer, and provide
+ necessary synchronization between clients accessing the same buffers.
+ This often involves evicting some objects from the GTT and re-binding
+ others (a fairly expensive operation), and providing relocation
+ support which hides fixed GTT offsets from clients. Clients must take
+ care not to submit command buffers that reference more objects than
+ can fit in the GTT; otherwise, GEM will reject them and no rendering
+ will occur. Similarly, if several objects in the buffer require fence
+ registers to be allocated for correct rendering (e.g. 2D blits on
+ pre-965 chips), care must be taken not to require more fence registers
+ than are available to the client. Such resource management should be
+ abstracted from the client in libdrm.
+ </para>
</sect3>
</sect2>
+ </sect1>
+
+ <!-- Internals: mode setting -->
+ <sect1 id="drm-mode-setting">
+ <title>Mode Setting</title>
+ <para>
+ Drivers must initialize the mode setting core by calling
+ <function>drm_mode_config_init</function> on the DRM device. The function
+ initializes the <structname>drm_device</structname>
+ <structfield>mode_config</structfield> field and never fails. Once done,
+ mode configuration must be setup by initializing the following fields.
+ </para>
+ <itemizedlist>
+ <listitem>
+ <synopsis>int min_width, min_height;
+int max_width, max_height;</synopsis>
+ <para>
+ Minimum and maximum width and height of the frame buffers in pixel
+ units.
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>struct drm_mode_config_funcs *funcs;</synopsis>
+ <para>Mode setting functions.</para>
+ </listitem>
+ </itemizedlist>
<sect2>
- <title>Output configuration</title>
+ <title>Frame Buffer Creation</title>
+ <synopsis>struct drm_framebuffer *(*fb_create)(struct drm_device *dev,
+ struct drm_file *file_priv,
+ struct drm_mode_fb_cmd2 *mode_cmd);</synopsis>
<para>
- The final initialization task is output configuration. This involves:
- <itemizedlist>
- <listitem>
- Finding and initializing the CRTCs, encoders, and connectors
- for the device.
- </listitem>
- <listitem>
- Creating an initial configuration.
- </listitem>
- <listitem>
- Registering a framebuffer console driver.
- </listitem>
- </itemizedlist>
+ Frame buffers are abstract memory objects that provide a source of
+ pixels to scanout to a CRTC. Applications explicitly request the
+ creation of frame buffers through the DRM_IOCTL_MODE_ADDFB(2) ioctls and
+ receive an opaque handle that can be passed to the KMS CRTC control,
+ plane configuration and page flip functions.
+ </para>
+ <para>
+ Frame buffers rely on the underneath memory manager for low-level memory
+ operations. When creating a frame buffer applications pass a memory
+ handle (or a list of memory handles for multi-planar formats) through
+ the <parameter>drm_mode_fb_cmd2</parameter> argument. This document
+ assumes that the driver uses GEM, those handles thus reference GEM
+ objects.
+ </para>
+ <para>
+ Drivers must first validate the requested frame buffer parameters passed
+ through the mode_cmd argument. In particular this is where invalid
+ sizes, pixel formats or pitches can be caught.
+ </para>
+ <para>
+ If the parameters are deemed valid, drivers then create, initialize and
+ return an instance of struct <structname>drm_framebuffer</structname>.
+ If desired the instance can be embedded in a larger driver-specific
+ structure. The new instance is initialized with a call to
+ <function>drm_framebuffer_init</function> which takes a pointer to DRM
+ frame buffer operations (struct
+ <structname>drm_framebuffer_funcs</structname>). Frame buffer operations are
+ <itemizedlist>
+ <listitem>
+ <synopsis>int (*create_handle)(struct drm_framebuffer *fb,
+ struct drm_file *file_priv, unsigned int *handle);</synopsis>
+ <para>
+ Create a handle to the frame buffer underlying memory object. If
+ the frame buffer uses a multi-plane format, the handle will
+ reference the memory object associated with the first plane.
+ </para>
+ <para>
+ Drivers call <function>drm_gem_handle_create</function> to create
+ the handle.
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>void (*destroy)(struct drm_framebuffer *framebuffer);</synopsis>
+ <para>
+ Destroy the frame buffer object and frees all associated
+ resources. Drivers must call
+ <function>drm_framebuffer_cleanup</function> to free resources
+ allocated by the DRM core for the frame buffer object, and must
+ make sure to unreference all memory objects associated with the
+ frame buffer. Handles created by the
+ <methodname>create_handle</methodname> operation are released by
+ the DRM core.
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>int (*dirty)(struct drm_framebuffer *framebuffer,
+ struct drm_file *file_priv, unsigned flags, unsigned color,
+ struct drm_clip_rect *clips, unsigned num_clips);</synopsis>
+ <para>
+ This optional operation notifies the driver that a region of the
+ frame buffer has changed in response to a DRM_IOCTL_MODE_DIRTYFB
+ ioctl call.
+ </para>
+ </listitem>
+ </itemizedlist>
+ </para>
+ <para>
+ After initializing the <structname>drm_framebuffer</structname>
+ instance drivers must fill its <structfield>width</structfield>,
+ <structfield>height</structfield>, <structfield>pitches</structfield>,
+ <structfield>offsets</structfield>, <structfield>depth</structfield>,
+ <structfield>bits_per_pixel</structfield> and
+ <structfield>pixel_format</structfield> fields from the values passed
+ through the <parameter>drm_mode_fb_cmd2</parameter> argument. They
+ should call the <function>drm_helper_mode_fill_fb_struct</function>
+ helper function to do so.
+ </para>
+ </sect2>
+ <sect2>
+ <title>Output Polling</title>
+ <synopsis>void (*output_poll_changed)(struct drm_device *dev);</synopsis>
+ <para>
+ This operation notifies the driver that the status of one or more
+ connectors has changed. Drivers that use the fb helper can just call the
+ <function>drm_fb_helper_hotplug_event</function> function to handle this
+ operation.
+ </para>
+ </sect2>
+ </sect1>
+
+ <!-- Internals: kms initialization and cleanup -->
+
+ <sect1 id="drm-kms-init">
+ <title>KMS Initialization and Cleanup</title>
+ <para>
+ A KMS device is abstracted and exposed as a set of planes, CRTCs, encoders
+ and connectors. KMS drivers must thus create and initialize all those
+ objects at load time after initializing mode setting.
+ </para>
+ <sect2>
+ <title>CRTCs (struct <structname>drm_crtc</structname>)</title>
+ <para>
+ A CRTC is an abstraction representing a part of the chip that contains a
+ pointer to a scanout buffer. Therefore, the number of CRTCs available
+ determines how many independent scanout buffers can be active at any
+ given time. The CRTC structure contains several fields to support this:
+ a pointer to some video memory (abstracted as a frame buffer object), a
+ display mode, and an (x, y) offset into the video memory to support
+ panning or configurations where one piece of video memory spans multiple
+ CRTCs.
</para>
<sect3>
- <title>Output discovery and initialization</title>
- <para>
- Several core functions exist to create CRTCs, encoders, and
- connectors, namely: drm_crtc_init(), drm_connector_init(), and
- drm_encoder_init(), along with several "helper" functions to
- perform common tasks.
- </para>
- <para>
- Connectors should be registered with sysfs once they've been
- detected and initialized, using the
- drm_sysfs_connector_add() function. Likewise, when they're
- removed from the system, they should be destroyed with
- drm_sysfs_connector_remove().
- </para>
- <programlisting>
-<![CDATA[
+ <title>CRTC Initialization</title>
+ <para>
+ A KMS device must create and register at least one struct
+ <structname>drm_crtc</structname> instance. The instance is allocated
+ and zeroed by the driver, possibly as part of a larger structure, and
+ registered with a call to <function>drm_crtc_init</function> with a
+ pointer to CRTC functions.
+ </para>
+ </sect3>
+ <sect3>
+ <title>CRTC Operations</title>
+ <sect4>
+ <title>Set Configuration</title>
+ <synopsis>int (*set_config)(struct drm_mode_set *set);</synopsis>
+ <para>
+ Apply a new CRTC configuration to the device. The configuration
+ specifies a CRTC, a frame buffer to scan out from, a (x,y) position in
+ the frame buffer, a display mode and an array of connectors to drive
+ with the CRTC if possible.
+ </para>
+ <para>
+ If the frame buffer specified in the configuration is NULL, the driver
+ must detach all encoders connected to the CRTC and all connectors
+ attached to those encoders and disable them.
+ </para>
+ <para>
+ This operation is called with the mode config lock held.
+ </para>
+ <note><para>
+ FIXME: How should set_config interact with DPMS? If the CRTC is
+ suspended, should it be resumed?
+ </para></note>
+ </sect4>
+ <sect4>
+ <title>Page Flipping</title>
+ <synopsis>int (*page_flip)(struct drm_crtc *crtc, struct drm_framebuffer *fb,
+ struct drm_pending_vblank_event *event);</synopsis>
+ <para>
+ Schedule a page flip to the given frame buffer for the CRTC. This
+ operation is called with the mode config mutex held.
+ </para>
+ <para>
+ Page flipping is a synchronization mechanism that replaces the frame
+ buffer being scanned out by the CRTC with a new frame buffer during
+ vertical blanking, avoiding tearing. When an application requests a page
+ flip the DRM core verifies that the new frame buffer is large enough to
+ be scanned out by the CRTC in the currently configured mode and then
+ calls the CRTC <methodname>page_flip</methodname> operation with a
+ pointer to the new frame buffer.
+ </para>
+ <para>
+ The <methodname>page_flip</methodname> operation schedules a page flip.
+ Once any pending rendering targetting the new frame buffer has
+ completed, the CRTC will be reprogrammed to display that frame buffer
+ after the next vertical refresh. The operation must return immediately
+ without waiting for rendering or page flip to complete and must block
+ any new rendering to the frame buffer until the page flip completes.
+ </para>
+ <para>
+ If a page flip is already pending, the
+ <methodname>page_flip</methodname> operation must return
+ -<errorname>EBUSY</errorname>.
+ </para>
+ <para>
+ To synchronize page flip to vertical blanking the driver will likely
+ need to enable vertical blanking interrupts. It should call
+ <function>drm_vblank_get</function> for that purpose, and call
+ <function>drm_vblank_put</function> after the page flip completes.
+ </para>
+ <para>
+ If the application has requested to be notified when page flip completes
+ the <methodname>page_flip</methodname> operation will be called with a
+ non-NULL <parameter>event</parameter> argument pointing to a
+ <structname>drm_pending_vblank_event</structname> instance. Upon page
+ flip completion the driver must fill the
+ <parameter>event</parameter>::<structfield>event</structfield>
+ <structfield>sequence</structfield>, <structfield>tv_sec</structfield>
+ and <structfield>tv_usec</structfield> fields with the associated
+ vertical blanking count and timestamp, add the event to the
+ <parameter>drm_file</parameter> list of events to be signaled, and wake
+ up any waiting process. This can be performed with
+ <programlisting><![CDATA[
+ struct timeval now;
+
+ event->event.sequence = drm_vblank_count_and_time(..., &now);
+ event->event.tv_sec = now.tv_sec;
+ event->event.tv_usec = now.tv_usec;
+
+ spin_lock_irqsave(&dev->event_lock, flags);
+ list_add_tail(&event->base.link, &event->base.file_priv->event_list);
+ wake_up_interruptible(&event->base.file_priv->event_wait);
+ spin_unlock_irqrestore(&dev->event_lock, flags);
+ ]]></programlisting>
+ </para>
+ <note><para>
+ FIXME: Could drivers that don't need to wait for rendering to complete
+ just add the event to <literal>dev->vblank_event_list</literal> and
+ let the DRM core handle everything, as for "normal" vertical blanking
+ events?
+ </para></note>
+ <para>
+ While waiting for the page flip to complete, the
+ <literal>event->base.link</literal> list head can be used freely by
+ the driver to store the pending event in a driver-specific list.
+ </para>
+ <para>
+ If the file handle is closed before the event is signaled, drivers must
+ take care to destroy the event in their
+ <methodname>preclose</methodname> operation (and, if needed, call
+ <function>drm_vblank_put</function>).
+ </para>
+ </sect4>
+ <sect4>
+ <title>Miscellaneous</title>
+ <itemizedlist>
+ <listitem>
+ <synopsis>void (*gamma_set)(struct drm_crtc *crtc, u16 *r, u16 *g, u16 *b,
+ uint32_t start, uint32_t size);</synopsis>
+ <para>
+ Apply a gamma table to the device. The operation is optional.
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>void (*destroy)(struct drm_crtc *crtc);</synopsis>
+ <para>
+ Destroy the CRTC when not needed anymore. See
+ <xref linkend="drm-kms-init"/>.
+ </para>
+ </listitem>
+ </itemizedlist>
+ </sect4>
+ </sect3>
+ </sect2>
+ <sect2>
+ <title>Planes (struct <structname>drm_plane</structname>)</title>
+ <para>
+ A plane represents an image source that can be blended with or overlayed
+ on top of a CRTC during the scanout process. Planes are associated with
+ a frame buffer to crop a portion of the image memory (source) and
+ optionally scale it to a destination size. The result is then blended
+ with or overlayed on top of a CRTC.
+ </para>
+ <sect3>
+ <title>Plane Initialization</title>
+ <para>
+ Planes are optional. To create a plane, a KMS drivers allocates and
+ zeroes an instances of struct <structname>drm_plane</structname>
+ (possibly as part of a larger structure) and registers it with a call
+ to <function>drm_plane_init</function>. The function takes a bitmask
+ of the CRTCs that can be associated with the plane, a pointer to the
+ plane functions and a list of format supported formats.
+ </para>
+ </sect3>
+ <sect3>
+ <title>Plane Operations</title>
+ <itemizedlist>
+ <listitem>
+ <synopsis>int (*update_plane)(struct drm_plane *plane, struct drm_crtc *crtc,
+ struct drm_framebuffer *fb, int crtc_x, int crtc_y,
+ unsigned int crtc_w, unsigned int crtc_h,
+ uint32_t src_x, uint32_t src_y,
+ uint32_t src_w, uint32_t src_h);</synopsis>
+ <para>
+ Enable and configure the plane to use the given CRTC and frame buffer.
+ </para>
+ <para>
+ The source rectangle in frame buffer memory coordinates is given by
+ the <parameter>src_x</parameter>, <parameter>src_y</parameter>,
+ <parameter>src_w</parameter> and <parameter>src_h</parameter>
+ parameters (as 16.16 fixed point values). Devices that don't support
+ subpixel plane coordinates can ignore the fractional part.
+ </para>
+ <para>
+ The destination rectangle in CRTC coordinates is given by the
+ <parameter>crtc_x</parameter>, <parameter>crtc_y</parameter>,
+ <parameter>crtc_w</parameter> and <parameter>crtc_h</parameter>
+ parameters (as integer values). Devices scale the source rectangle to
+ the destination rectangle. If scaling is not supported, and the source
+ rectangle size doesn't match the destination rectangle size, the
+ driver must return a -<errorname>EINVAL</errorname> error.
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>int (*disable_plane)(struct drm_plane *plane);</synopsis>
+ <para>
+ Disable the plane. The DRM core calls this method in response to a
+ DRM_IOCTL_MODE_SETPLANE ioctl call with the frame buffer ID set to 0.
+ Disabled planes must not be processed by the CRTC.
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>void (*destroy)(struct drm_plane *plane);</synopsis>
+ <para>
+ Destroy the plane when not needed anymore. See
+ <xref linkend="drm-kms-init"/>.
+ </para>
+ </listitem>
+ </itemizedlist>
+ </sect3>
+ </sect2>
+ <sect2>
+ <title>Encoders (struct <structname>drm_encoder</structname>)</title>
+ <para>
+ An encoder takes pixel data from a CRTC and converts it to a format
+ suitable for any attached connectors. On some devices, it may be
+ possible to have a CRTC send data to more than one encoder. In that
+ case, both encoders would receive data from the same scanout buffer,
+ resulting in a "cloned" display configuration across the connectors
+ attached to each encoder.
+ </para>
+ <sect3>
+ <title>Encoder Initialization</title>
+ <para>
+ As for CRTCs, a KMS driver must create, initialize and register at
+ least one struct <structname>drm_encoder</structname> instance. The
+ instance is allocated and zeroed by the driver, possibly as part of a
+ larger structure.
+ </para>
+ <para>
+ Drivers must initialize the struct <structname>drm_encoder</structname>
+ <structfield>possible_crtcs</structfield> and
+ <structfield>possible_clones</structfield> fields before registering the
+ encoder. Both fields are bitmasks of respectively the CRTCs that the
+ encoder can be connected to, and sibling encoders candidate for cloning.
+ </para>
+ <para>
+ After being initialized, the encoder must be registered with a call to
+ <function>drm_encoder_init</function>. The function takes a pointer to
+ the encoder functions and an encoder type. Supported types are
+ <itemizedlist>
+ <listitem>
+ DRM_MODE_ENCODER_DAC for VGA and analog on DVI-I/DVI-A
+ </listitem>
+ <listitem>
+ DRM_MODE_ENCODER_TMDS for DVI, HDMI and (embedded) DisplayPort
+ </listitem>
+ <listitem>
+ DRM_MODE_ENCODER_LVDS for display panels
+ </listitem>
+ <listitem>
+ DRM_MODE_ENCODER_TVDAC for TV output (Composite, S-Video, Component,
+ SCART)
+ </listitem>
+ <listitem>
+ DRM_MODE_ENCODER_VIRTUAL for virtual machine displays
+ </listitem>
+ </itemizedlist>
+ </para>
+ <para>
+ Encoders must be attached to a CRTC to be used. DRM drivers leave
+ encoders unattached at initialization time. Applications (or the fbdev
+ compatibility layer when implemented) are responsible for attaching the
+ encoders they want to use to a CRTC.
+ </para>
+ </sect3>
+ <sect3>
+ <title>Encoder Operations</title>
+ <itemizedlist>
+ <listitem>
+ <synopsis>void (*destroy)(struct drm_encoder *encoder);</synopsis>
+ <para>
+ Called to destroy the encoder when not needed anymore. See
+ <xref linkend="drm-kms-init"/>.
+ </para>
+ </listitem>
+ </itemizedlist>
+ </sect3>
+ </sect2>
+ <sect2>
+ <title>Connectors (struct <structname>drm_connector</structname>)</title>
+ <para>
+ A connector is the final destination for pixel data on a device, and
+ usually connects directly to an external display device like a monitor
+ or laptop panel. A connector can only be attached to one encoder at a
+ time. The connector is also the structure where information about the
+ attached display is kept, so it contains fields for display data, EDID
+ data, DPMS & connection status, and information about modes
+ supported on the attached displays.
+ </para>
+ <sect3>
+ <title>Connector Initialization</title>
+ <para>
+ Finally a KMS driver must create, initialize, register and attach at
+ least one struct <structname>drm_connector</structname> instance. The
+ instance is created as other KMS objects and initialized by setting the
+ following fields.
+ </para>
+ <variablelist>
+ <varlistentry>
+ <term><structfield>interlace_allowed</structfield></term>
+ <listitem><para>
+ Whether the connector can handle interlaced modes.
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><structfield>doublescan_allowed</structfield></term>
+ <listitem><para>
+ Whether the connector can handle doublescan.
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><structfield>display_info
+ </structfield></term>
+ <listitem><para>
+ Display information is filled from EDID information when a display
+ is detected. For non hot-pluggable displays such as flat panels in
+ embedded systems, the driver should initialize the
+ <structfield>display_info</structfield>.<structfield>width_mm</structfield>
+ and
+ <structfield>display_info</structfield>.<structfield>height_mm</structfield>
+ fields with the physical size of the display.
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term id="drm-kms-connector-polled"><structfield>polled</structfield></term>
+ <listitem><para>
+ Connector polling mode, a combination of
+ <variablelist>
+ <varlistentry>
+ <term>DRM_CONNECTOR_POLL_HPD</term>
+ <listitem><para>
+ The connector generates hotplug events and doesn't need to be
+ periodically polled. The CONNECT and DISCONNECT flags must not
+ be set together with the HPD flag.
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_CONNECTOR_POLL_CONNECT</term>
+ <listitem><para>
+ Periodically poll the connector for connection.
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_CONNECTOR_POLL_DISCONNECT</term>
+ <listitem><para>
+ Periodically poll the connector for disconnection.
+ </para></listitem>
+ </varlistentry>
+ </variablelist>
+ Set to 0 for connectors that don't support connection status
+ discovery.
+ </para></listitem>
+ </varlistentry>
+ </variablelist>
+ <para>
+ The connector is then registered with a call to
+ <function>drm_connector_init</function> with a pointer to the connector
+ functions and a connector type, and exposed through sysfs with a call to
+ <function>drm_sysfs_connector_add</function>.
+ </para>
+ <para>
+ Supported connector types are
+ <itemizedlist>
+ <listitem>DRM_MODE_CONNECTOR_VGA</listitem>
+ <listitem>DRM_MODE_CONNECTOR_DVII</listitem>
+ <listitem>DRM_MODE_CONNECTOR_DVID</listitem>
+ <listitem>DRM_MODE_CONNECTOR_DVIA</listitem>
+ <listitem>DRM_MODE_CONNECTOR_Composite</listitem>
+ <listitem>DRM_MODE_CONNECTOR_SVIDEO</listitem>
+ <listitem>DRM_MODE_CONNECTOR_LVDS</listitem>
+ <listitem>DRM_MODE_CONNECTOR_Component</listitem>
+ <listitem>DRM_MODE_CONNECTOR_9PinDIN</listitem>
+ <listitem>DRM_MODE_CONNECTOR_DisplayPort</listitem>
+ <listitem>DRM_MODE_CONNECTOR_HDMIA</listitem>
+ <listitem>DRM_MODE_CONNECTOR_HDMIB</listitem>
+ <listitem>DRM_MODE_CONNECTOR_TV</listitem>
+ <listitem>DRM_MODE_CONNECTOR_eDP</listitem>
+ <listitem>DRM_MODE_CONNECTOR_VIRTUAL</listitem>
+ </itemizedlist>
+ </para>
+ <para>
+ Connectors must be attached to an encoder to be used. For devices that
+ map connectors to encoders 1:1, the connector should be attached at
+ initialization time with a call to
+ <function>drm_mode_connector_attach_encoder</function>. The driver must
+ also set the <structname>drm_connector</structname>
+ <structfield>encoder</structfield> field to point to the attached
+ encoder.
+ </para>
+ <para>
+ Finally, drivers must initialize the connectors state change detection
+ with a call to <function>drm_kms_helper_poll_init</function>. If at
+ least one connector is pollable but can't generate hotplug interrupts
+ (indicated by the DRM_CONNECTOR_POLL_CONNECT and
+ DRM_CONNECTOR_POLL_DISCONNECT connector flags), a delayed work will
+ automatically be queued to periodically poll for changes. Connectors
+ that can generate hotplug interrupts must be marked with the
+ DRM_CONNECTOR_POLL_HPD flag instead, and their interrupt handler must
+ call <function>drm_helper_hpd_irq_event</function>. The function will
+ queue a delayed work to check the state of all connectors, but no
+ periodic polling will be done.
+ </para>
+ </sect3>
+ <sect3>
+ <title>Connector Operations</title>
+ <note><para>
+ Unless otherwise state, all operations are mandatory.
+ </para></note>
+ <sect4>
+ <title>DPMS</title>
+ <synopsis>void (*dpms)(struct drm_connector *connector, int mode);</synopsis>
+ <para>
+ The DPMS operation sets the power state of a connector. The mode
+ argument is one of
+ <itemizedlist>
+ <listitem><para>DRM_MODE_DPMS_ON</para></listitem>
+ <listitem><para>DRM_MODE_DPMS_STANDBY</para></listitem>
+ <listitem><para>DRM_MODE_DPMS_SUSPEND</para></listitem>
+ <listitem><para>DRM_MODE_DPMS_OFF</para></listitem>
+ </itemizedlist>
+ </para>
+ <para>
+ In all but DPMS_ON mode the encoder to which the connector is attached
+ should put the display in low-power mode by driving its signals
+ appropriately. If more than one connector is attached to the encoder
+ care should be taken not to change the power state of other displays as
+ a side effect. Low-power mode should be propagated to the encoders and
+ CRTCs when all related connectors are put in low-power mode.
+ </para>
+ </sect4>
+ <sect4>
+ <title>Modes</title>
+ <synopsis>int (*fill_modes)(struct drm_connector *connector, uint32_t max_width,
+ uint32_t max_height);</synopsis>
+ <para>
+ Fill the mode list with all supported modes for the connector. If the
+ <parameter>max_width</parameter> and <parameter>max_height</parameter>
+ arguments are non-zero, the implementation must ignore all modes wider
+ than <parameter>max_width</parameter> or higher than
+ <parameter>max_height</parameter>.
+ </para>
+ <para>
+ The connector must also fill in this operation its
+ <structfield>display_info</structfield>
+ <structfield>width_mm</structfield> and
+ <structfield>height_mm</structfield> fields with the connected display
+ physical size in millimeters. The fields should be set to 0 if the value
+ isn't known or is not applicable (for instance for projector devices).
+ </para>
+ </sect4>
+ <sect4>
+ <title>Connection Status</title>
+ <para>
+ The connection status is updated through polling or hotplug events when
+ supported (see <xref linkend="drm-kms-connector-polled"/>). The status
+ value is reported to userspace through ioctls and must not be used
+ inside the driver, as it only gets initialized by a call to
+ <function>drm_mode_getconnector</function> from userspace.
+ </para>
+ <synopsis>enum drm_connector_status (*detect)(struct drm_connector *connector,
+ bool force);</synopsis>
+ <para>
+ Check to see if anything is attached to the connector. The
+ <parameter>force</parameter> parameter is set to false whilst polling or
+ to true when checking the connector due to user request.
+ <parameter>force</parameter> can be used by the driver to avoid
+ expensive, destructive operations during automated probing.
+ </para>
+ <para>
+ Return connector_status_connected if something is connected to the
+ connector, connector_status_disconnected if nothing is connected and
+ connector_status_unknown if the connection state isn't known.
+ </para>
+ <para>
+ Drivers should only return connector_status_connected if the connection
+ status has really been probed as connected. Connectors that can't detect
+ the connection status, or failed connection status probes, should return
+ connector_status_unknown.
+ </para>
+ </sect4>
+ <sect4>
+ <title>Miscellaneous</title>
+ <itemizedlist>
+ <listitem>
+ <synopsis>void (*destroy)(struct drm_connector *connector);</synopsis>
+ <para>
+ Destroy the connector when not needed anymore. See
+ <xref linkend="drm-kms-init"/>.
+ </para>
+ </listitem>
+ </itemizedlist>
+ </sect4>
+ </sect3>
+ </sect2>
+ <sect2>
+ <title>Cleanup</title>
+ <para>
+ The DRM core manages its objects' lifetime. When an object is not needed
+ anymore the core calls its destroy function, which must clean up and
+ free every resource allocated for the object. Every
+ <function>drm_*_init</function> call must be matched with a
+ corresponding <function>drm_*_cleanup</function> call to cleanup CRTCs
+ (<function>drm_crtc_cleanup</function>), planes
+ (<function>drm_plane_cleanup</function>), encoders
+ (<function>drm_encoder_cleanup</function>) and connectors
+ (<function>drm_connector_cleanup</function>). Furthermore, connectors
+ that have been added to sysfs must be removed by a call to
+ <function>drm_sysfs_connector_remove</function> before calling
+ <function>drm_connector_cleanup</function>.
+ </para>
+ <para>
+ Connectors state change detection must be cleanup up with a call to
+ <function>drm_kms_helper_poll_fini</function>.
+ </para>
+ </sect2>
+ <sect2>
+ <title>Output discovery and initialization example</title>
+ <programlisting><![CDATA[
void intel_crt_init(struct drm_device *dev)
{
struct drm_connector *connector;
drm_connector_helper_add(connector, &intel_crt_connector_helper_funcs);
drm_sysfs_connector_add(connector);
-}
-]]>
- </programlisting>
- <para>
- In the example above (again, taken from the i915 driver), a
- CRT connector and encoder combination is created. A device-specific
- i2c bus is also created for fetching EDID data and
- performing monitor detection. Once the process is complete,
- the new connector is registered with sysfs to make its
- properties available to applications.
- </para>
- <sect4>
- <title>Helper functions and core functions</title>
- <para>
- Since many PC-class graphics devices have similar display output
- designs, the DRM provides a set of helper functions to make
- output management easier. The core helper routines handle
- encoder re-routing and the disabling of unused functions following
- mode setting. Using the helpers is optional, but recommended for
- devices with PC-style architectures (i.e. a set of display planes
- for feeding pixels to encoders which are in turn routed to
- connectors). Devices with more complex requirements needing
- finer grained management may opt to use the core callbacks
- directly.
- </para>
- <para>
- [Insert typical diagram here.] [Insert OMAP style config here.]
- </para>
- </sect4>
- <para>
- Each encoder object needs to provide:
- <itemizedlist>
- <listitem>
- A DPMS (basically on/off) function.
- </listitem>
- <listitem>
- A mode-fixup function (for converting requested modes into
- native hardware timings).
- </listitem>
- <listitem>
- Functions (prepare, set, and commit) for use by the core DRM
- helper functions.
- </listitem>
- </itemizedlist>
- Connector helpers need to provide functions (mode-fetch, validity,
- and encoder-matching) for returning an ideal encoder for a given
- connector. The core connector functions include a DPMS callback,
- save/restore routines (deprecated), detection, mode probing,
- property handling, and cleanup functions.
- </para>
-<!--!Edrivers/char/drm/drm_crtc.h-->
-<!--!Edrivers/char/drm/drm_crtc.c-->
-<!--!Edrivers/char/drm/drm_crtc_helper.c-->
- </sect3>
+}]]></programlisting>
+ <para>
+ In the example above (taken from the i915 driver), a CRTC, connector and
+ encoder combination is created. A device-specific i2c bus is also
+ created for fetching EDID data and performing monitor detection. Once
+ the process is complete, the new connector is registered with sysfs to
+ make its properties available to applications.
+ </para>
</sect2>
</sect1>
- <!-- Internals: vblank handling -->
+ <!-- Internals: mid-layer helper functions -->
<sect1>
- <title>VBlank event handling</title>
+ <title>Mid-layer Helper Functions</title>
<para>
- The DRM core exposes two vertical blank related ioctls:
- <variablelist>
- <varlistentry>
- <term>DRM_IOCTL_WAIT_VBLANK</term>
- <listitem>
- <para>
- This takes a struct drm_wait_vblank structure as its argument,
- and it is used to block or request a signal when a specified
- vblank event occurs.
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term>DRM_IOCTL_MODESET_CTL</term>
- <listitem>
- <para>
- This should be called by application level drivers before and
- after mode setting, since on many devices the vertical blank
- counter is reset at that time. Internally, the DRM snapshots
- the last vblank count when the ioctl is called with the
- _DRM_PRE_MODESET command, so that the counter won't go backwards
- (which is dealt with when _DRM_POST_MODESET is used).
- </para>
- </listitem>
- </varlistentry>
- </variablelist>
-<!--!Edrivers/char/drm/drm_irq.c-->
+ The CRTC, encoder and connector functions provided by the drivers
+ implement the DRM API. They're called by the DRM core and ioctl handlers
+ to handle device state changes and configuration request. As implementing
+ those functions often requires logic not specific to drivers, mid-layer
+ helper functions are available to avoid duplicating boilerplate code.
+ </para>
+ <para>
+ The DRM core contains one mid-layer implementation. The mid-layer provides
+ implementations of several CRTC, encoder and connector functions (called
+ from the top of the mid-layer) that pre-process requests and call
+ lower-level functions provided by the driver (at the bottom of the
+ mid-layer). For instance, the
+ <function>drm_crtc_helper_set_config</function> function can be used to
+ fill the struct <structname>drm_crtc_funcs</structname>
+ <structfield>set_config</structfield> field. When called, it will split
+ the <methodname>set_config</methodname> operation in smaller, simpler
+ operations and call the driver to handle them.
</para>
<para>
- To support the functions above, the DRM core provides several
- helper functions for tracking vertical blank counters, and
- requires drivers to provide several callbacks:
- get_vblank_counter(), enable_vblank() and disable_vblank(). The
- core uses get_vblank_counter() to keep the counter accurate
- across interrupt disable periods. It should return the current
- vertical blank event count, which is often tracked in a device
- register. The enable and disable vblank callbacks should enable
- and disable vertical blank interrupts, respectively. In the
- absence of DRM clients waiting on vblank events, the core DRM
- code uses the disable_vblank() function to disable
- interrupts, which saves power. They are re-enabled again when
- a client calls the vblank wait ioctl above.
+ To use the mid-layer, drivers call <function>drm_crtc_helper_add</function>,
+ <function>drm_encoder_helper_add</function> and
+ <function>drm_connector_helper_add</function> functions to install their
+ mid-layer bottom operations handlers, and fill the
+ <structname>drm_crtc_funcs</structname>,
+ <structname>drm_encoder_funcs</structname> and
+ <structname>drm_connector_funcs</structname> structures with pointers to
+ the mid-layer top API functions. Installing the mid-layer bottom operation
+ handlers is best done right after registering the corresponding KMS object.
</para>
<para>
- A device that doesn't provide a count register may simply use an
- internal atomic counter incremented on every vertical blank
- interrupt (and then treat the enable_vblank() and disable_vblank()
- callbacks as no-ops).
+ The mid-layer is not split between CRTC, encoder and connector operations.
+ To use it, a driver must provide bottom functions for all of the three KMS
+ entities.
</para>
+ <sect2>
+ <title>Helper Functions</title>
+ <itemizedlist>
+ <listitem>
+ <synopsis>int drm_crtc_helper_set_config(struct drm_mode_set *set);</synopsis>
+ <para>
+ The <function>drm_crtc_helper_set_config</function> helper function
+ is a CRTC <methodname>set_config</methodname> implementation. It
+ first tries to locate the best encoder for each connector by calling
+ the connector <methodname>best_encoder</methodname> helper
+ operation.
+ </para>
+ <para>
+ After locating the appropriate encoders, the helper function will
+ call the <methodname>mode_fixup</methodname> encoder and CRTC helper
+ operations to adjust the requested mode, or reject it completely in
+ which case an error will be returned to the application. If the new
+ configuration after mode adjustment is identical to the current
+ configuration the helper function will return without performing any
+ other operation.
+ </para>
+ <para>
+ If the adjusted mode is identical to the current mode but changes to
+ the frame buffer need to be applied, the
+ <function>drm_crtc_helper_set_config</function> function will call
+ the CRTC <methodname>mode_set_base</methodname> helper operation. If
+ the adjusted mode differs from the current mode, or if the
+ <methodname>mode_set_base</methodname> helper operation is not
+ provided, the helper function performs a full mode set sequence by
+ calling the <methodname>prepare</methodname>,
+ <methodname>mode_set</methodname> and
+ <methodname>commit</methodname> CRTC and encoder helper operations,
+ in that order.
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>void drm_helper_connector_dpms(struct drm_connector *connector, int mode);</synopsis>
+ <para>
+ The <function>drm_helper_connector_dpms</function> helper function
+ is a connector <methodname>dpms</methodname> implementation that
+ tracks power state of connectors. To use the function, drivers must
+ provide <methodname>dpms</methodname> helper operations for CRTCs
+ and encoders to apply the DPMS state to the device.
+ </para>
+ <para>
+ The mid-layer doesn't track the power state of CRTCs and encoders.
+ The <methodname>dpms</methodname> helper operations can thus be
+ called with a mode identical to the currently active mode.
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
+ uint32_t maxX, uint32_t maxY);</synopsis>
+ <para>
+ The <function>drm_helper_probe_single_connector_modes</function> helper
+ function is a connector <methodname>fill_modes</methodname>
+ implementation that updates the connection status for the connector
+ and then retrieves a list of modes by calling the connector
+ <methodname>get_modes</methodname> helper operation.
+ </para>
+ <para>
+ The function filters out modes larger than
+ <parameter>max_width</parameter> and <parameter>max_height</parameter>
+ if specified. It then calls the connector
+ <methodname>mode_valid</methodname> helper operation for each mode in
+ the probed list to check whether the mode is valid for the connector.
+ </para>
+ </listitem>
+ </itemizedlist>
+ </sect2>
+ <sect2>
+ <title>CRTC Helper Operations</title>
+ <itemizedlist>
+ <listitem id="drm-helper-crtc-mode-fixup">
+ <synopsis>bool (*mode_fixup)(struct drm_crtc *crtc,
+ const struct drm_display_mode *mode,
+ struct drm_display_mode *adjusted_mode);</synopsis>
+ <para>
+ Let CRTCs adjust the requested mode or reject it completely. This
+ operation returns true if the mode is accepted (possibly after being
+ adjusted) or false if it is rejected.
+ </para>
+ <para>
+ The <methodname>mode_fixup</methodname> operation should reject the
+ mode if it can't reasonably use it. The definition of "reasonable"
+ is currently fuzzy in this context. One possible behaviour would be
+ to set the adjusted mode to the panel timings when a fixed-mode
+ panel is used with hardware capable of scaling. Another behaviour
+ would be to accept any input mode and adjust it to the closest mode
+ supported by the hardware (FIXME: This needs to be clarified).
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>int (*mode_set_base)(struct drm_crtc *crtc, int x, int y,
+ struct drm_framebuffer *old_fb)</synopsis>
+ <para>
+ Move the CRTC on the current frame buffer (stored in
+ <literal>crtc->fb</literal>) to position (x,y). Any of the frame
+ buffer, x position or y position may have been modified.
+ </para>
+ <para>
+ This helper operation is optional. If not provided, the
+ <function>drm_crtc_helper_set_config</function> function will fall
+ back to the <methodname>mode_set</methodname> helper operation.
+ </para>
+ <note><para>
+ FIXME: Why are x and y passed as arguments, as they can be accessed
+ through <literal>crtc->x</literal> and
+ <literal>crtc->y</literal>?
+ </para></note>
+ </listitem>
+ <listitem>
+ <synopsis>void (*prepare)(struct drm_crtc *crtc);</synopsis>
+ <para>
+ Prepare the CRTC for mode setting. This operation is called after
+ validating the requested mode. Drivers use it to perform
+ device-specific operations required before setting the new mode.
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>int (*mode_set)(struct drm_crtc *crtc, struct drm_display_mode *mode,
+ struct drm_display_mode *adjusted_mode, int x, int y,
+ struct drm_framebuffer *old_fb);</synopsis>
+ <para>
+ Set a new mode, position and frame buffer. Depending on the device
+ requirements, the mode can be stored internally by the driver and
+ applied in the <methodname>commit</methodname> operation, or
+ programmed to the hardware immediately.
+ </para>
+ <para>
+ The <methodname>mode_set</methodname> operation returns 0 on success
+ or a negative error code if an error occurs.
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>void (*commit)(struct drm_crtc *crtc);</synopsis>
+ <para>
+ Commit a mode. This operation is called after setting the new mode.
+ Upon return the device must use the new mode and be fully
+ operational.
+ </para>
+ </listitem>
+ </itemizedlist>
+ </sect2>
+ <sect2>
+ <title>Encoder Helper Operations</title>
+ <itemizedlist>
+ <listitem>
+ <synopsis>bool (*mode_fixup)(struct drm_encoder *encoder,
+ const struct drm_display_mode *mode,
+ struct drm_display_mode *adjusted_mode);</synopsis>
+ <note><para>
+ FIXME: The mode argument be const, but the i915 driver modifies
+ mode->clock in <function>intel_dp_mode_fixup</function>.
+ </para></note>
+ <para>
+ Let encoders adjust the requested mode or reject it completely. This
+ operation returns true if the mode is accepted (possibly after being
+ adjusted) or false if it is rejected. See the
+ <link linkend="drm-helper-crtc-mode-fixup">mode_fixup CRTC helper
+ operation</link> for an explanation of the allowed adjustments.
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>void (*prepare)(struct drm_encoder *encoder);</synopsis>
+ <para>
+ Prepare the encoder for mode setting. This operation is called after
+ validating the requested mode. Drivers use it to perform
+ device-specific operations required before setting the new mode.
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>void (*mode_set)(struct drm_encoder *encoder,
+ struct drm_display_mode *mode,
+ struct drm_display_mode *adjusted_mode);</synopsis>
+ <para>
+ Set a new mode. Depending on the device requirements, the mode can
+ be stored internally by the driver and applied in the
+ <methodname>commit</methodname> operation, or programmed to the
+ hardware immediately.
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>void (*commit)(struct drm_encoder *encoder);</synopsis>
+ <para>
+ Commit a mode. This operation is called after setting the new mode.
+ Upon return the device must use the new mode and be fully
+ operational.
+ </para>
+ </listitem>
+ </itemizedlist>
+ </sect2>
+ <sect2>
+ <title>Connector Helper Operations</title>
+ <itemizedlist>
+ <listitem>
+ <synopsis>struct drm_encoder *(*best_encoder)(struct drm_connector *connector);</synopsis>
+ <para>
+ Return a pointer to the best encoder for the connecter. Device that
+ map connectors to encoders 1:1 simply return the pointer to the
+ associated encoder. This operation is mandatory.
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>int (*get_modes)(struct drm_connector *connector);</synopsis>
+ <para>
+ Fill the connector's <structfield>probed_modes</structfield> list
+ by parsing EDID data with <function>drm_add_edid_modes</function> or
+ calling <function>drm_mode_probed_add</function> directly for every
+ supported mode and return the number of modes it has detected. This
+ operation is mandatory.
+ </para>
+ <para>
+ When adding modes manually the driver creates each mode with a call to
+ <function>drm_mode_create</function> and must fill the following fields.
+ <itemizedlist>
+ <listitem>
+ <synopsis>__u32 type;</synopsis>
+ <para>
+ Mode type bitmask, a combination of
+ <variablelist>
+ <varlistentry>
+ <term>DRM_MODE_TYPE_BUILTIN</term>
+ <listitem><para>not used?</para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_MODE_TYPE_CLOCK_C</term>
+ <listitem><para>not used?</para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_MODE_TYPE_CRTC_C</term>
+ <listitem><para>not used?</para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>
+ DRM_MODE_TYPE_PREFERRED - The preferred mode for the connector
+ </term>
+ <listitem>
+ <para>not used?</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_MODE_TYPE_DEFAULT</term>
+ <listitem><para>not used?</para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_MODE_TYPE_USERDEF</term>
+ <listitem><para>not used?</para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_MODE_TYPE_DRIVER</term>
+ <listitem>
+ <para>
+ The mode has been created by the driver (as opposed to
+ to user-created modes).
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ Drivers must set the DRM_MODE_TYPE_DRIVER bit for all modes they
+ create, and set the DRM_MODE_TYPE_PREFERRED bit for the preferred
+ mode.
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>__u32 clock;</synopsis>
+ <para>Pixel clock frequency in kHz unit</para>
+ </listitem>
+ <listitem>
+ <synopsis>__u16 hdisplay, hsync_start, hsync_end, htotal;
+ __u16 vdisplay, vsync_start, vsync_end, vtotal;</synopsis>
+ <para>Horizontal and vertical timing information</para>
+ <screen><![CDATA[
+ Active Front Sync Back
+ Region Porch Porch
+ <-----------------------><----------------><-------------><-------------->
+
+ //////////////////////|
+ ////////////////////// |
+ ////////////////////// |.................. ................
+ _______________
+
+ <----- [hv]display ----->
+ <------------- [hv]sync_start ------------>
+ <--------------------- [hv]sync_end --------------------->
+ <-------------------------------- [hv]total ----------------------------->
+]]></screen>
+ </listitem>
+ <listitem>
+ <synopsis>__u16 hskew;
+ __u16 vscan;</synopsis>
+ <para>Unknown</para>
+ </listitem>
+ <listitem>
+ <synopsis>__u32 flags;</synopsis>
+ <para>
+ Mode flags, a combination of
+ <variablelist>
+ <varlistentry>
+ <term>DRM_MODE_FLAG_PHSYNC</term>
+ <listitem><para>
+ Horizontal sync is active high
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_MODE_FLAG_NHSYNC</term>
+ <listitem><para>
+ Horizontal sync is active low
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_MODE_FLAG_PVSYNC</term>
+ <listitem><para>
+ Vertical sync is active high
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_MODE_FLAG_NVSYNC</term>
+ <listitem><para>
+ Vertical sync is active low
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_MODE_FLAG_INTERLACE</term>
+ <listitem><para>
+ Mode is interlaced
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_MODE_FLAG_DBLSCAN</term>
+ <listitem><para>
+ Mode uses doublescan
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_MODE_FLAG_CSYNC</term>
+ <listitem><para>
+ Mode uses composite sync
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_MODE_FLAG_PCSYNC</term>
+ <listitem><para>
+ Composite sync is active high
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_MODE_FLAG_NCSYNC</term>
+ <listitem><para>
+ Composite sync is active low
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_MODE_FLAG_HSKEW</term>
+ <listitem><para>
+ hskew provided (not used?)
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_MODE_FLAG_BCAST</term>
+ <listitem><para>
+ not used?
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_MODE_FLAG_PIXMUX</term>
+ <listitem><para>
+ not used?
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_MODE_FLAG_DBLCLK</term>
+ <listitem><para>
+ not used?
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_MODE_FLAG_CLKDIV2</term>
+ <listitem><para>
+ ?
+ </para></listitem>
+ </varlistentry>
+ </variablelist>
+ </para>
+ <para>
+ Note that modes marked with the INTERLACE or DBLSCAN flags will be
+ filtered out by
+ <function>drm_helper_probe_single_connector_modes</function> if
+ the connector's <structfield>interlace_allowed</structfield> or
+ <structfield>doublescan_allowed</structfield> field is set to 0.
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>char name[DRM_DISPLAY_MODE_LEN];</synopsis>
+ <para>
+ Mode name. The driver must call
+ <function>drm_mode_set_name</function> to fill the mode name from
+ <structfield>hdisplay</structfield>,
+ <structfield>vdisplay</structfield> and interlace flag after
+ filling the corresponding fields.
+ </para>
+ </listitem>
+ </itemizedlist>
+ </para>
+ <para>
+ The <structfield>vrefresh</structfield> value is computed by
+ <function>drm_helper_probe_single_connector_modes</function>.
+ </para>
+ <para>
+ When parsing EDID data, <function>drm_add_edid_modes</function> fill the
+ connector <structfield>display_info</structfield>
+ <structfield>width_mm</structfield> and
+ <structfield>height_mm</structfield> fields. When creating modes
+ manually the <methodname>get_modes</methodname> helper operation must
+ set the <structfield>display_info</structfield>
+ <structfield>width_mm</structfield> and
+ <structfield>height_mm</structfield> fields if they haven't been set
+ already (for instance at initilization time when a fixed-size panel is
+ attached to the connector). The mode <structfield>width_mm</structfield>
+ and <structfield>height_mm</structfield> fields are only used internally
+ during EDID parsing and should not be set when creating modes manually.
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>int (*mode_valid)(struct drm_connector *connector,
+ struct drm_display_mode *mode);</synopsis>
+ <para>
+ Verify whether a mode is valid for the connector. Return MODE_OK for
+ supported modes and one of the enum drm_mode_status values (MODE_*)
+ for unsupported modes. This operation is mandatory.
+ </para>
+ <para>
+ As the mode rejection reason is currently not used beside for
+ immediately removing the unsupported mode, an implementation can
+ return MODE_BAD regardless of the exact reason why the mode is not
+ valid.
+ </para>
+ <note><para>
+ Note that the <methodname>mode_valid</methodname> helper operation is
+ only called for modes detected by the device, and
+ <emphasis>not</emphasis> for modes set by the user through the CRTC
+ <methodname>set_config</methodname> operation.
+ </para></note>
+ </listitem>
+ </itemizedlist>
+ </sect2>
</sect1>
- <sect1>
- <title>Memory management</title>
+ <!-- Internals: vertical blanking -->
+
+ <sect1 id="drm-vertical-blank">
+ <title>Vertical Blanking</title>
+ <para>
+ Vertical blanking plays a major role in graphics rendering. To achieve
+ tear-free display, users must synchronize page flips and/or rendering to
+ vertical blanking. The DRM API offers ioctls to perform page flips
+ synchronized to vertical blanking and wait for vertical blanking.
+ </para>
+ <para>
+ The DRM core handles most of the vertical blanking management logic, which
+ involves filtering out spurious interrupts, keeping race-free blanking
+ counters, coping with counter wrap-around and resets and keeping use
+ counts. It relies on the driver to generate vertical blanking interrupts
+ and optionally provide a hardware vertical blanking counter. Drivers must
+ implement the following operations.
+ </para>
+ <itemizedlist>
+ <listitem>
+ <synopsis>int (*enable_vblank) (struct drm_device *dev, int crtc);
+void (*disable_vblank) (struct drm_device *dev, int crtc);</synopsis>
+ <para>
+ Enable or disable vertical blanking interrupts for the given CRTC.
+ </para>
+ </listitem>
+ <listitem>
+ <synopsis>u32 (*get_vblank_counter) (struct drm_device *dev, int crtc);</synopsis>
+ <para>
+ Retrieve the value of the vertical blanking counter for the given
+ CRTC. If the hardware maintains a vertical blanking counter its value
+ should be returned. Otherwise drivers can use the
+ <function>drm_vblank_count</function> helper function to handle this
+ operation.
+ </para>
+ </listitem>
+ </itemizedlist>
<para>
- The memory manager lies at the heart of many DRM operations; it
- is required to support advanced client features like OpenGL
- pbuffers. The DRM currently contains two memory managers: TTM
- and GEM.
+ Drivers must initialize the vertical blanking handling core with a call to
+ <function>drm_vblank_init</function> in their
+ <methodname>load</methodname> operation. The function will set the struct
+ <structname>drm_device</structname>
+ <structfield>vblank_disable_allowed</structfield> field to 0. This will
+ keep vertical blanking interrupts enabled permanently until the first mode
+ set operation, where <structfield>vblank_disable_allowed</structfield> is
+ set to 1. The reason behind this is not clear. Drivers can set the field
+ to 1 after <function>calling drm_vblank_init</function> to make vertical
+ blanking interrupts dynamically managed from the beginning.
</para>
+ <para>
+ Vertical blanking interrupts can be enabled by the DRM core or by drivers
+ themselves (for instance to handle page flipping operations). The DRM core
+ maintains a vertical blanking use count to ensure that the interrupts are
+ not disabled while a user still needs them. To increment the use count,
+ drivers call <function>drm_vblank_get</function>. Upon return vertical
+ blanking interrupts are guaranteed to be enabled.
+ </para>
+ <para>
+ To decrement the use count drivers call
+ <function>drm_vblank_put</function>. Only when the use count drops to zero
+ will the DRM core disable the vertical blanking interrupts after a delay
+ by scheduling a timer. The delay is accessible through the vblankoffdelay
+ module parameter or the <varname>drm_vblank_offdelay</varname> global
+ variable and expressed in milliseconds. Its default value is 5000 ms.
+ </para>
+ <para>
+ When a vertical blanking interrupt occurs drivers only need to call the
+ <function>drm_handle_vblank</function> function to account for the
+ interrupt.
+ </para>
+ <para>
+ Resources allocated by <function>drm_vblank_init</function> must be freed
+ with a call to <function>drm_vblank_cleanup</function> in the driver
+ <methodname>unload</methodname> operation handler.
+ </para>
+ </sect1>
+
+ <!-- Internals: open/close, file operations and ioctls -->
+ <sect1>
+ <title>Open/Close, File Operations and IOCTLs</title>
<sect2>
- <title>The Translation Table Manager (TTM)</title>
+ <title>Open and Close</title>
+ <synopsis>int (*firstopen) (struct drm_device *);
+void (*lastclose) (struct drm_device *);
+int (*open) (struct drm_device *, struct drm_file *);
+void (*preclose) (struct drm_device *, struct drm_file *);
+void (*postclose) (struct drm_device *, struct drm_file *);</synopsis>
+ <abstract>Open and close handlers. None of those methods are mandatory.
+ </abstract>
<para>
- TTM was developed by Tungsten Graphics, primarily by Thomas
- Hellström, and is intended to be a flexible, high performance
- graphics memory manager.
+ The <methodname>firstopen</methodname> method is called by the DRM core
+ when an application opens a device that has no other opened file handle.
+ Similarly the <methodname>lastclose</methodname> method is called when
+ the last application holding a file handle opened on the device closes
+ it. Both methods are mostly used for UMS (User Mode Setting) drivers to
+ acquire and release device resources which should be done in the
+ <methodname>load</methodname> and <methodname>unload</methodname>
+ methods for KMS drivers.
</para>
<para>
- Drivers wishing to support TTM must fill out a drm_bo_driver
- structure.
+ Note that the <methodname>lastclose</methodname> method is also called
+ at module unload time or, for hot-pluggable devices, when the device is
+ unplugged. The <methodname>firstopen</methodname> and
+ <methodname>lastclose</methodname> calls can thus be unbalanced.
</para>
<para>
- TTM design background and information belongs here.
+ The <methodname>open</methodname> method is called every time the device
+ is opened by an application. Drivers can allocate per-file private data
+ in this method and store them in the struct
+ <structname>drm_file</structname> <structfield>driver_priv</structfield>
+ field. Note that the <methodname>open</methodname> method is called
+ before <methodname>firstopen</methodname>.
+ </para>
+ <para>
+ The close operation is split into <methodname>preclose</methodname> and
+ <methodname>postclose</methodname> methods. Drivers must stop and
+ cleanup all per-file operations in the <methodname>preclose</methodname>
+ method. For instance pending vertical blanking and page flip events must
+ be cancelled. No per-file operation is allowed on the file handle after
+ returning from the <methodname>preclose</methodname> method.
+ </para>
+ <para>
+ Finally the <methodname>postclose</methodname> method is called as the
+ last step of the close operation, right before calling the
+ <methodname>lastclose</methodname> method if no other open file handle
+ exists for the device. Drivers that have allocated per-file private data
+ in the <methodname>open</methodname> method should free it here.
+ </para>
+ <para>
+ The <methodname>lastclose</methodname> method should restore CRTC and
+ plane properties to default value, so that a subsequent open of the
+ device will not inherit state from the previous user.
</para>
</sect2>
-
<sect2>
- <title>The Graphics Execution Manager (GEM)</title>
+ <title>File Operations</title>
+ <synopsis>const struct file_operations *fops</synopsis>
+ <abstract>File operations for the DRM device node.</abstract>
<para>
- GEM is an Intel project, authored by Eric Anholt and Keith
- Packard. It provides simpler interfaces than TTM, and is well
- suited for UMA devices.
+ Drivers must define the file operations structure that forms the DRM
+ userspace API entry point, even though most of those operations are
+ implemented in the DRM core. The <methodname>open</methodname>,
+ <methodname>release</methodname> and <methodname>ioctl</methodname>
+ operations are handled by
+ <programlisting>
+ .owner = THIS_MODULE,
+ .open = drm_open,
+ .release = drm_release,
+ .unlocked_ioctl = drm_ioctl,
+ #ifdef CONFIG_COMPAT
+ .compat_ioctl = drm_compat_ioctl,
+ #endif
+ </programlisting>
</para>
<para>
- GEM-enabled drivers must provide gem_init_object() and
- gem_free_object() callbacks to support the core memory
- allocation routines. They should also provide several driver-specific
- ioctls to support command execution, pinning, buffer
- read & write, mapping, and domain ownership transfers.
+ Drivers that implement private ioctls that requires 32/64bit
+ compatibility support must provide their own
+ <methodname>compat_ioctl</methodname> handler that processes private
+ ioctls and calls <function>drm_compat_ioctl</function> for core ioctls.
</para>
<para>
- On a fundamental level, GEM involves several operations:
- <itemizedlist>
- <listitem>Memory allocation and freeing</listitem>
- <listitem>Command execution</listitem>
- <listitem>Aperture management at command execution time</listitem>
- </itemizedlist>
- Buffer object allocation is relatively
- straightforward and largely provided by Linux's shmem layer, which
- provides memory to back each object. When mapped into the GTT
- or used in a command buffer, the backing pages for an object are
- flushed to memory and marked write combined so as to be coherent
- with the GPU. Likewise, if the CPU accesses an object after the GPU
- has finished rendering to the object, then the object must be made
- coherent with the CPU's view
- of memory, usually involving GPU cache flushing of various kinds.
- This core CPU<->GPU coherency management is provided by a
- device-specific ioctl, which evaluates an object's current domain and
- performs any necessary flushing or synchronization to put the object
- into the desired coherency domain (note that the object may be busy,
- i.e. an active render target; in that case, setting the domain
- blocks the client and waits for rendering to complete before
- performing any necessary flushing operations).
- </para>
- <para>
- Perhaps the most important GEM function is providing a command
- execution interface to clients. Client programs construct command
- buffers containing references to previously allocated memory objects,
- and then submit them to GEM. At that point, GEM takes care to bind
- all the objects into the GTT, execute the buffer, and provide
- necessary synchronization between clients accessing the same buffers.
- This often involves evicting some objects from the GTT and re-binding
- others (a fairly expensive operation), and providing relocation
- support which hides fixed GTT offsets from clients. Clients must
- take care not to submit command buffers that reference more objects
- than can fit in the GTT; otherwise, GEM will reject them and no rendering
- will occur. Similarly, if several objects in the buffer require
- fence registers to be allocated for correct rendering (e.g. 2D blits
- on pre-965 chips), care must be taken not to require more fence
- registers than are available to the client. Such resource management
- should be abstracted from the client in libdrm.
+ The <methodname>read</methodname> and <methodname>poll</methodname>
+ operations provide support for reading DRM events and polling them. They
+ are implemented by
+ <programlisting>
+ .poll = drm_poll,
+ .read = drm_read,
+ .fasync = drm_fasync,
+ .llseek = no_llseek,
+ </programlisting>
+ </para>
+ <para>
+ The memory mapping implementation varies depending on how the driver
+ manages memory. Pre-GEM drivers will use <function>drm_mmap</function>,
+ while GEM-aware drivers will use <function>drm_gem_mmap</function>. See
+ <xref linkend="drm-gem"/>.
+ <programlisting>
+ .mmap = drm_gem_mmap,
+ </programlisting>
+ </para>
+ <para>
+ No other file operation is supported by the DRM API.
+ </para>
+ </sect2>
+ <sect2>
+ <title>IOCTLs</title>
+ <synopsis>struct drm_ioctl_desc *ioctls;
+int num_ioctls;</synopsis>
+ <abstract>Driver-specific ioctls descriptors table.</abstract>
+ <para>
+ Driver-specific ioctls numbers start at DRM_COMMAND_BASE. The ioctls
+ descriptors table is indexed by the ioctl number offset from the base
+ value. Drivers can use the DRM_IOCTL_DEF_DRV() macro to initialize the
+ table entries.
+ </para>
+ <para>
+ <programlisting>DRM_IOCTL_DEF_DRV(ioctl, func, flags)</programlisting>
+ <para>
+ <parameter>ioctl</parameter> is the ioctl name. Drivers must define
+ the DRM_##ioctl and DRM_IOCTL_##ioctl macros to the ioctl number
+ offset from DRM_COMMAND_BASE and the ioctl number respectively. The
+ first macro is private to the device while the second must be exposed
+ to userspace in a public header.
+ </para>
+ <para>
+ <parameter>func</parameter> is a pointer to the ioctl handler function
+ compatible with the <type>drm_ioctl_t</type> type.
+ <programlisting>typedef int drm_ioctl_t(struct drm_device *dev, void *data,
+ struct drm_file *file_priv);</programlisting>
+ </para>
+ <para>
+ <parameter>flags</parameter> is a bitmask combination of the following
+ values. It restricts how the ioctl is allowed to be called.
+ <itemizedlist>
+ <listitem><para>
+ DRM_AUTH - Only authenticated callers allowed
+ </para></listitem>
+ <listitem><para>
+ DRM_MASTER - The ioctl can only be called on the master file
+ handle
+ </para></listitem>
+ <listitem><para>
+ DRM_ROOT_ONLY - Only callers with the SYSADMIN capability allowed
+ </para></listitem>
+ <listitem><para>
+ DRM_CONTROL_ALLOW - The ioctl can only be called on a control
+ device
+ </para></listitem>
+ <listitem><para>
+ DRM_UNLOCKED - The ioctl handler will be called without locking
+ the DRM global mutex
+ </para></listitem>
+ </itemizedlist>
+ </para>
</para>
</sect2>
-
- </sect1>
-
- <!-- Output management -->
- <sect1>
- <title>Output management</title>
- <para>
- At the core of the DRM output management code is a set of
- structures representing CRTCs, encoders, and connectors.
- </para>
- <para>
- A CRTC is an abstraction representing a part of the chip that
- contains a pointer to a scanout buffer. Therefore, the number
- of CRTCs available determines how many independent scanout
- buffers can be active at any given time. The CRTC structure
- contains several fields to support this: a pointer to some video
- memory, a display mode, and an (x, y) offset into the video
- memory to support panning or configurations where one piece of
- video memory spans multiple CRTCs.
- </para>
- <para>
- An encoder takes pixel data from a CRTC and converts it to a
- format suitable for any attached connectors. On some devices,
- it may be possible to have a CRTC send data to more than one
- encoder. In that case, both encoders would receive data from
- the same scanout buffer, resulting in a "cloned" display
- configuration across the connectors attached to each encoder.
- </para>
- <para>
- A connector is the final destination for pixel data on a device,
- and usually connects directly to an external display device like
- a monitor or laptop panel. A connector can only be attached to
- one encoder at a time. The connector is also the structure
- where information about the attached display is kept, so it
- contains fields for display data, EDID data, DPMS &
- connection status, and information about modes supported on the
- attached displays.
- </para>
-<!--!Edrivers/char/drm/drm_crtc.c-->
- </sect1>
-
- <sect1>
- <title>Framebuffer management</title>
- <para>
- Clients need to provide a framebuffer object which provides a source
- of pixels for a CRTC to deliver to the encoder(s) and ultimately the
- connector(s). A framebuffer is fundamentally a driver-specific memory
- object, made into an opaque handle by the DRM's addfb() function.
- Once a framebuffer has been created this way, it may be passed to the
- KMS mode setting routines for use in a completed configuration.
- </para>
</sect1>
<sect1>
</para>
</sect1>
+ <!-- Internals: suspend/resume -->
+
<sect1>
- <title>Suspend/resume</title>
+ <title>Suspend/Resume</title>
+ <para>
+ The DRM core provides some suspend/resume code, but drivers wanting full
+ suspend/resume support should provide save() and restore() functions.
+ These are called at suspend, hibernate, or resume time, and should perform
+ any state save or restore required by your device across suspend or
+ hibernate states.
+ </para>
+ <synopsis>int (*suspend) (struct drm_device *, pm_message_t state);
+int (*resume) (struct drm_device *);</synopsis>
<para>
- The DRM core provides some suspend/resume code, but drivers
- wanting full suspend/resume support should provide save() and
- restore() functions. These are called at suspend,
- hibernate, or resume time, and should perform any state save or
- restore required by your device across suspend or hibernate
- states.
+ Those are legacy suspend and resume methods. New driver should use the
+ power management interface provided by their bus type (usually through
+ the struct <structname>device_driver</structname> dev_pm_ops) and set
+ these methods to NULL.
</para>
</sect1>
</sect1>
</chapter>
+<!-- TODO
+
+- Add a glossary
+- Document the struct_mutex catch-all lock
+- Document connector properties
+
+- Why is the load method optional?
+- What are drivers supposed to set the initial display state to, and how?
+ Connector's DPMS states are not initialized and are thus equal to
+ DRM_MODE_DPMS_ON. The fbcon compatibility layer calls
+ drm_helper_disable_unused_functions(), which disables unused encoders and
+ CRTCs, but doesn't touch the connectors' DPMS state, and
+ drm_helper_connector_dpms() in reaction to fbdev blanking events. Do drivers
+ that don't implement (or just don't use) fbcon compatibility need to call
+ those functions themselves?
+- KMS drivers must call drm_vblank_pre_modeset() and drm_vblank_post_modeset()
+ around mode setting. Should this be done in the DRM core?
+- vblank_disable_allowed is set to 1 in the first drm_vblank_post_modeset()
+ call and never set back to 0. It seems to be safe to permanently set it to 1
+ in drm_vblank_init() for KMS driver, and it might be safe for UMS drivers as
+ well. This should be investigated.
+- crtc and connector .save and .restore operations are only used internally in
+ drivers, should they be removed from the core?
+- encoder mid-layer .save and .restore operations are only used internally in
+ drivers, should they be removed from the core?
+- encoder mid-layer .detect operation is only used internally in drivers,
+ should it be removed from the core?
+-->
+
<!-- External interfaces -->
<chapter id="drmExternals">
Cover generic ioctls and sysfs layout here. We only need high-level
info, since man pages should cover the rest.
</para>
+
+ <!-- External: vblank handling -->
+
+ <sect1>
+ <title>VBlank event handling</title>
+ <para>
+ The DRM core exposes two vertical blank related ioctls:
+ <variablelist>
+ <varlistentry>
+ <term>DRM_IOCTL_WAIT_VBLANK</term>
+ <listitem>
+ <para>
+ This takes a struct drm_wait_vblank structure as its argument,
+ and it is used to block or request a signal when a specified
+ vblank event occurs.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>DRM_IOCTL_MODESET_CTL</term>
+ <listitem>
+ <para>
+ This should be called by application level drivers before and
+ after mode setting, since on many devices the vertical blank
+ counter is reset at that time. Internally, the DRM snapshots
+ the last vblank count when the ioctl is called with the
+ _DRM_PRE_MODESET command, so that the counter won't go backwards
+ (which is dealt with when _DRM_POST_MODESET is used).
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+<!--!Edrivers/char/drm/drm_irq.c-->
+ </para>
+ </sect1>
+
</chapter>
<!-- API reference -->
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