-----------
Uclass - a group of devices which operate in the same way. A uclass provides
- a way of accessing invidual devices within the group, but always
+ a way of accessing individual devices within the group, but always
using the same interface. For example a GPIO uclass provides
operations for get/set value. An I2C uclass may have 10 I2C ports,
4 with one driver, and 6 with another.
Build U-Boot sandbox and run it:
- make sandbox_config
+ make sandbox_defconfig
make
- ./u-boot
+ ./u-boot -d u-boot.dtb
(type 'reset' to exit U-Boot)
You should see something like this:
<...U-Boot banner...>
- Running 12 driver model tests
+ Running 29 driver model tests
Test: dm_test_autobind
Test: dm_test_autoprobe
+ Test: dm_test_bus_children
+ Device 'd-test': seq 3 is in use by 'b-test'
+ Device 'c-test@0': seq 0 is in use by 'a-test'
+ Device 'c-test@1': seq 1 is in use by 'd-test'
+ Test: dm_test_bus_children_funcs
+ Test: dm_test_bus_children_iterators
+ Test: dm_test_bus_parent_data
+ Test: dm_test_bus_parent_ops
Test: dm_test_children
Test: dm_test_fdt
+ Device 'd-test': seq 3 is in use by 'b-test'
+ Test: dm_test_fdt_offset
+ Test: dm_test_fdt_pre_reloc
+ Test: dm_test_fdt_uclass_seq
+ Device 'd-test': seq 3 is in use by 'b-test'
+ Device 'a-test': seq 0 is in use by 'd-test'
Test: dm_test_gpio
- sandbox_gpio: sb_gpio_get_value: error: offset 4 not reserved
+ extra-gpios: get_value: error: gpio b5 not reserved
+ Test: dm_test_gpio_anon
+ Test: dm_test_gpio_copy
+ Test: dm_test_gpio_leak
+ extra-gpios: get_value: error: gpio b5 not reserved
+ Test: dm_test_gpio_requestf
Test: dm_test_leak
- Warning: Please add '#define DEBUG' to the top of common/dlmalloc.c
- Warning: Please add '#define DEBUG' to the top of common/dlmalloc.c
Test: dm_test_lifecycle
Test: dm_test_operations
Test: dm_test_ordering
Test: dm_test_platdata
+ Test: dm_test_pre_reloc
Test: dm_test_remove
+ Test: dm_test_spi_find
+ Invalid chip select 0:0 (err=-19)
+ SF: Failed to get idcodes
+ Device 'name-emul': seq 0 is in use by 'name-emul'
+ SF: Detected M25P16 with page size 256 Bytes, erase size 64 KiB, total 2 MiB
+ Test: dm_test_spi_flash
+ 2097152 bytes written in 0 ms
+ SF: Detected M25P16 with page size 256 Bytes, erase size 64 KiB, total 2 MiB
+ SPI flash test:
+ 0 erase: 0 ticks, 65536000 KiB/s 524288.000 Mbps
+ 1 check: 0 ticks, 65536000 KiB/s 524288.000 Mbps
+ 2 write: 0 ticks, 65536000 KiB/s 524288.000 Mbps
+ 3 read: 0 ticks, 65536000 KiB/s 524288.000 Mbps
+ Test passed
+ 0 erase: 0 ticks, 65536000 KiB/s 524288.000 Mbps
+ 1 check: 0 ticks, 65536000 KiB/s 524288.000 Mbps
+ 2 write: 0 ticks, 65536000 KiB/s 524288.000 Mbps
+ 3 read: 0 ticks, 65536000 KiB/s 524288.000 Mbps
+ Test: dm_test_spi_xfer
+ SF: Detected M25P16 with page size 256 Bytes, erase size 64 KiB, total 2 MiB
Test: dm_test_uclass
+ Test: dm_test_uclass_before_ready
Failures: 0
-(You can add '#define DEBUG' as suggested to check for memory leaks)
-
What is going on?
-----------------
Let's start at the top. The demo command is in common/cmd_demo.c. It does
-the usual command procesing and then:
+the usual command processing and then:
struct udevice *demo_dev;
Platform Data
-------------
-Where does the platform data come from? See demo-pdata.c which
+Platform data is like Linux platform data, if you are familiar with that.
+It provides the board-specific information to start up a device.
+
+Why is this information not just stored in the device driver itself? The
+idea is that the device driver is generic, and can in principle operate on
+any board that has that type of device. For example, with modern
+highly-complex SoCs it is common for the IP to come from an IP vendor, and
+therefore (for example) the MMC controller may be the same on chips from
+different vendors. It makes no sense to write independent drivers for the
+MMC controller on each vendor's SoC, when they are all almost the same.
+Similarly, we may have 6 UARTs in an SoC, all of which are mostly the same,
+but lie at different addresses in the address space.
+
+Using the UART example, we have a single driver and it is instantiated 6
+times by supplying 6 lots of platform data. Each lot of platform data
+gives the driver name and a pointer to a structure containing information
+about this instance - e.g. the address of the register space. It may be that
+one of the UARTS supports RS-485 operation - this can be added as a flag in
+the platform data, which is set for this one port and clear for the rest.
+
+Think of your driver as a generic piece of code which knows how to talk to
+a device, but needs to know where it is, any variant/option information and
+so on. Platform data provides this link between the generic piece of code
+and the specific way it is bound on a particular board.
+
+Examples of platform data include:
+
+ - The base address of the IP block's register space
+ - Configuration options, like:
+ - the SPI polarity and maximum speed for a SPI controller
+ - the I2C speed to use for an I2C device
+ - the number of GPIOs available in a GPIO device
+
+Where does the platform data come from? It is either held in a structure
+which is compiled into U-Boot, or it can be parsed from the Device Tree
+(see 'Device Tree' below).
+
+For an example of how it can be compiled in, see demo-pdata.c which
sets up a table of driver names and their associated platform data.
The data can be interpreted by the drivers however they like - it is
basically a communication scheme between the board-specific code and
the generic drivers, which are intended to work on any board.
-Drivers can acceess their data via dev->info->platdata. Here is
+Drivers can access their data via dev->info->platdata. Here is
the declaration for the platform data, which would normally appear
in the board file.
sides = <4>;
};
+This means that instead of having lots of U_BOOT_DEVICE() declarations in
+the board file, we put these in the device tree. This approach allows a lot
+more generality, since the same board file can support many types of boards
+(e,g. with the same SoC) just by using different device trees. An added
+benefit is that the Linux device tree can be used, thus further simplifying
+the task of board-bring up either for U-Boot or Linux devs (whoever gets to
+the board first!).
The easiest way to make this work it to add a few members to the driver:
.platdata_auto_alloc_size = sizeof(struct dm_test_pdata),
.ofdata_to_platdata = testfdt_ofdata_to_platdata,
- .probe = testfdt_drv_probe,
The 'auto_alloc' feature allowed space for the platdata to be allocated
-and zeroed before the driver's ofdata_to_platdata method is called. This
-method reads the information out of the device tree and puts it in
-dev->platdata. Then the probe method is called to set up the device.
+and zeroed before the driver's ofdata_to_platdata() method is called. The
+ofdata_to_platdata() method, which the driver write supplies, should parse
+the device tree node for this device and place it in dev->platdata. Thus
+when the probe method is called later (to set up the device ready for use)
+the platform data will be present.
Note that both methods are optional. If you provide an ofdata_to_platdata
-method then it wlil be called first (after bind). If you provide a probe
-method it will be called next.
+method then it will be called first (during activation). If you provide a
+probe method it will be called next. See Driver Lifecycle below for more
+details.
If you don't want to have the platdata automatically allocated then you
can leave out platdata_auto_alloc_size. In this case you can use malloc
in your ofdata_to_platdata (or probe) method to allocate the required memory,
and you should free it in the remove method.
+The driver model tree is intended to mirror that of the device tree. The
+root driver is at device tree offset 0 (the root node, '/'), and its
+children are the children of the root node.
+
Declaring Uclasses
------------------
end of the enum there, then declare your uclass as above.
+Device Sequence Numbers
+-----------------------
+
+U-Boot numbers devices from 0 in many situations, such as in the command
+line for I2C and SPI buses, and the device names for serial ports (serial0,
+serial1, ...). Driver model supports this numbering and permits devices
+to be locating by their 'sequence'. This numbering uniquely identifies a
+device in its uclass, so no two devices within a particular uclass can have
+the same sequence number.
+
+Sequence numbers start from 0 but gaps are permitted. For example, a board
+may have I2C buses 1, 4, 5 but no 0, 2 or 3. The choice of how devices are
+numbered is up to a particular board, and may be set by the SoC in some
+cases. While it might be tempting to automatically renumber the devices
+where there are gaps in the sequence, this can lead to confusion and is
+not the way that U-Boot works.
+
+Each device can request a sequence number. If none is required then the
+device will be automatically allocated the next available sequence number.
+
+To specify the sequence number in the device tree an alias is typically
+used. Make sure that the uclass has the DM_UC_FLAG_SEQ_ALIAS flag set.
+
+aliases {
+ serial2 = "/serial@22230000";
+};
+
+This indicates that in the uclass called "serial", the named node
+("/serial@22230000") will be given sequence number 2. Any command or driver
+which requests serial device 2 will obtain this device.
+
+More commonly you can use node references, which expand to the full path:
+
+aliases {
+ serial2 = &serial_2;
+};
+...
+serial_2: serial@22230000 {
+...
+};
+
+The alias resolves to the same string in this case, but this version is
+easier to read.
+
+Device sequence numbers are resolved when a device is probed. Before then
+the sequence number is only a request which may or may not be honoured,
+depending on what other devices have been probed. However the numbering is
+entirely under the control of the board author so a conflict is generally
+an error.
+
+
+Bus Drivers
+-----------
+
+A common use of driver model is to implement a bus, a device which provides
+access to other devices. Example of buses include SPI and I2C. Typically
+the bus provides some sort of transport or translation that makes it
+possible to talk to the devices on the bus.
+
+Driver model provides some useful features to help with implementing buses.
+Firstly, a bus can request that its children store some 'parent data' which
+can be used to keep track of child state. Secondly, the bus can define
+methods which are called when a child is probed or removed. This is similar
+to the methods the uclass driver provides. Thirdly, per-child platform data
+can be provided to specify things like the child's address on the bus. This
+persists across child probe()/remove() cycles.
+
+For consistency and ease of implementation, the bus uclass can specify the
+per-child platform data, so that it can be the same for all children of buses
+in that uclass. There are also uclass methods which can be called when
+children are bound and probed.
+
+Here an explanation of how a bus fits with a uclass may be useful. Consider
+a USB bus with several devices attached to it, each from a different (made
+up) uclass:
+
+ xhci_usb (UCLASS_USB)
+ eth (UCLASS_ETHERNET)
+ camera (UCLASS_CAMERA)
+ flash (UCLASS_FLASH_STORAGE)
+
+Each of the devices is connected to a different address on the USB bus.
+The bus device wants to store this address and some other information such
+as the bus speed for each device.
+
+To achieve this, the bus device can use dev->parent_platdata in each of its
+three children. This can be auto-allocated if the bus driver (or bus uclass)
+has a non-zero value for per_child_platdata_auto_alloc_size. If not, then
+the bus device or uclass can allocate the space itself before the child
+device is probed.
+
+Also the bus driver can define the child_pre_probe() and child_post_remove()
+methods to allow it to do some processing before the child is activated or
+after it is deactivated.
+
+Similarly the bus uclass can define the child_post_bind() method to obtain
+the per-child platform data from the device tree and set it up for the child.
+The bus uclass can also provide a child_pre_probe() method. Very often it is
+the bus uclass that controls these features, since it avoids each driver
+having to do the same processing. Of course the driver can still tweak and
+override these activities.
+
+Note that the information that controls this behaviour is in the bus's
+driver, not the child's. In fact it is possible that child has no knowledge
+that it is connected to a bus. The same child device may even be used on two
+different bus types. As an example. the 'flash' device shown above may also
+be connected on a SATA bus or standalone with no bus:
+
+ xhci_usb (UCLASS_USB)
+ flash (UCLASS_FLASH_STORAGE) - parent data/methods defined by USB bus
+
+ sata (UCLASS_SATA)
+ flash (UCLASS_FLASH_STORAGE) - parent data/methods defined by SATA bus
+
+ flash (UCLASS_FLASH_STORAGE) - no parent data/methods (not on a bus)
+
+Above you can see that the driver for xhci_usb/sata controls the child's
+bus methods. In the third example the device is not on a bus, and therefore
+will not have these methods at all. Consider the case where the flash
+device defines child methods. These would be used for *its* children, and
+would be quite separate from the methods defined by the driver for the bus
+that the flash device is connetced to. The act of attaching a device to a
+parent device which is a bus, causes the device to start behaving like a
+bus device, regardless of its own views on the matter.
+
+The uclass for the device can also contain data private to that uclass.
+But note that each device on the bus may be a memeber of a different
+uclass, and this data has nothing to do with the child data for each child
+on the bus. It is the bus' uclass that controls the child with respect to
+the bus.
+
+
+Driver Lifecycle
+----------------
+
+Here are the stages that a device goes through in driver model. Note that all
+methods mentioned here are optional - e.g. if there is no probe() method for
+a device then it will not be called. A simple device may have very few
+methods actually defined.
+
+1. Bind stage
+
+A device and its driver are bound using one of these two methods:
+
+ - Scan the U_BOOT_DEVICE() definitions. U-Boot It looks up the
+name specified by each, to find the appropriate driver. It then calls
+device_bind() to create a new device and bind' it to its driver. This will
+call the device's bind() method.
+
+ - Scan through the device tree definitions. U-Boot looks at top-level
+nodes in the the device tree. It looks at the compatible string in each node
+and uses the of_match part of the U_BOOT_DRIVER() structure to find the
+right driver for each node. It then calls device_bind() to bind the
+newly-created device to its driver (thereby creating a device structure).
+This will also call the device's bind() method.
+
+At this point all the devices are known, and bound to their drivers. There
+is a 'struct udevice' allocated for all devices. However, nothing has been
+activated (except for the root device). Each bound device that was created
+from a U_BOOT_DEVICE() declaration will hold the platdata pointer specified
+in that declaration. For a bound device created from the device tree,
+platdata will be NULL, but of_offset will be the offset of the device tree
+node that caused the device to be created. The uclass is set correctly for
+the device.
+
+The device's bind() method is permitted to perform simple actions, but
+should not scan the device tree node, not initialise hardware, nor set up
+structures or allocate memory. All of these tasks should be left for
+the probe() method.
+
+Note that compared to Linux, U-Boot's driver model has a separate step of
+probe/remove which is independent of bind/unbind. This is partly because in
+U-Boot it may be expensive to probe devices and we don't want to do it until
+they are needed, or perhaps until after relocation.
+
+2. Activation/probe
+
+When a device needs to be used, U-Boot activates it, by following these
+steps (see device_probe()):
+
+ a. If priv_auto_alloc_size is non-zero, then the device-private space
+ is allocated for the device and zeroed. It will be accessible as
+ dev->priv. The driver can put anything it likes in there, but should use
+ it for run-time information, not platform data (which should be static
+ and known before the device is probed).
+
+ b. If platdata_auto_alloc_size is non-zero, then the platform data space
+ is allocated. This is only useful for device tree operation, since
+ otherwise you would have to specific the platform data in the
+ U_BOOT_DEVICE() declaration. The space is allocated for the device and
+ zeroed. It will be accessible as dev->platdata.
+
+ c. If the device's uclass specifies a non-zero per_device_auto_alloc_size,
+ then this space is allocated and zeroed also. It is allocated for and
+ stored in the device, but it is uclass data. owned by the uclass driver.
+ It is possible for the device to access it.
+
+ d. If the device's immediate parent specifies a per_child_auto_alloc_size
+ then this space is allocated. This is intended for use by the parent
+ device to keep track of things related to the child. For example a USB
+ flash stick attached to a USB host controller would likely use this
+ space. The controller can hold information about the USB state of each
+ of its children.
+
+ e. All parent devices are probed. It is not possible to activate a device
+ unless its predecessors (all the way up to the root device) are activated.
+ This means (for example) that an I2C driver will require that its bus
+ be activated.
+
+ f. The device's sequence number is assigned, either the requested one
+ (assuming no conflicts) or the next available one if there is a conflict
+ or nothing particular is requested.
+
+ g. If the driver provides an ofdata_to_platdata() method, then this is
+ called to convert the device tree data into platform data. This should
+ do various calls like fdtdec_get_int(gd->fdt_blob, dev->of_offset, ...)
+ to access the node and store the resulting information into dev->platdata.
+ After this point, the device works the same way whether it was bound
+ using a device tree node or U_BOOT_DEVICE() structure. In either case,
+ the platform data is now stored in the platdata structure. Typically you
+ will use the platdata_auto_alloc_size feature to specify the size of the
+ platform data structure, and U-Boot will automatically allocate and zero
+ it for you before entry to ofdata_to_platdata(). But if not, you can
+ allocate it yourself in ofdata_to_platdata(). Note that it is preferable
+ to do all the device tree decoding in ofdata_to_platdata() rather than
+ in probe(). (Apart from the ugliness of mixing configuration and run-time
+ data, one day it is possible that U-Boot will cache platformat data for
+ devices which are regularly de/activated).
+
+ h. The device's probe() method is called. This should do anything that
+ is required by the device to get it going. This could include checking
+ that the hardware is actually present, setting up clocks for the
+ hardware and setting up hardware registers to initial values. The code
+ in probe() can access:
+
+ - platform data in dev->platdata (for configuration)
+ - private data in dev->priv (for run-time state)
+ - uclass data in dev->uclass_priv (for things the uclass stores
+ about this device)
+
+ Note: If you don't use priv_auto_alloc_size then you will need to
+ allocate the priv space here yourself. The same applies also to
+ platdata_auto_alloc_size. Remember to free them in the remove() method.
+
+ i. The device is marked 'activated'
+
+ j. The uclass's post_probe() method is called, if one exists. This may
+ cause the uclass to do some housekeeping to record the device as
+ activated and 'known' by the uclass.
+
+3. Running stage
+
+The device is now activated and can be used. From now until it is removed
+all of the above structures are accessible. The device appears in the
+uclass's list of devices (so if the device is in UCLASS_GPIO it will appear
+as a device in the GPIO uclass). This is the 'running' state of the device.
+
+4. Removal stage
+
+When the device is no-longer required, you can call device_remove() to
+remove it. This performs the probe steps in reverse:
+
+ a. The uclass's pre_remove() method is called, if one exists. This may
+ cause the uclass to do some housekeeping to record the device as
+ deactivated and no-longer 'known' by the uclass.
+
+ b. All the device's children are removed. It is not permitted to have
+ an active child device with a non-active parent. This means that
+ device_remove() is called for all the children recursively at this point.
+
+ c. The device's remove() method is called. At this stage nothing has been
+ deallocated so platform data, private data and the uclass data will all
+ still be present. This is where the hardware can be shut down. It is
+ intended that the device be completely inactive at this point, For U-Boot
+ to be sure that no hardware is running, it should be enough to remove
+ all devices.
+
+ d. The device memory is freed (platform data, private data, uclass data,
+ parent data).
+
+ Note: Because the platform data for a U_BOOT_DEVICE() is defined with a
+ static pointer, it is not de-allocated during the remove() method. For
+ a device instantiated using the device tree data, the platform data will
+ be dynamically allocated, and thus needs to be deallocated during the
+ remove() method, either:
+
+ 1. if the platdata_auto_alloc_size is non-zero, the deallocation
+ happens automatically within the driver model core; or
+
+ 2. when platdata_auto_alloc_size is 0, both the allocation (in probe()
+ or preferably ofdata_to_platdata()) and the deallocation in remove()
+ are the responsibility of the driver author.
+
+ e. The device sequence number is set to -1, meaning that it no longer
+ has an allocated sequence. If the device is later reactivated and that
+ sequence number is still free, it may well receive the name sequence
+ number again. But from this point, the sequence number previously used
+ by this device will no longer exist (think of SPI bus 2 being removed
+ and bus 2 is no longer available for use).
+
+ f. The device is marked inactive. Note that it is still bound, so the
+ device structure itself is not freed at this point. Should the device be
+ activated again, then the cycle starts again at step 2 above.
+
+5. Unbind stage
+
+The device is unbound. This is the step that actually destroys the device.
+If a parent has children these will be destroyed first. After this point
+the device does not exist and its memory has be deallocated.
+
+
Data Structures
---------------
For the record, this implementation uses a very similar approach to the
original patches, but makes at least the following changes:
-- Tried to agressively remove boilerplate, so that for most drivers there
+- Tried to aggressively remove boilerplate, so that for most drivers there
is little or no 'driver model' code to write.
- Moved some data from code into data structure - e.g. store a pointer to
the driver operations structure in the driver, rather than passing it
to the driver bind function.
-- Rename some structures to make them more similar to Linux (struct device
+- Rename some structures to make them more similar to Linux (struct udevice
instead of struct instance, struct platdata, etc.)
- Change the name 'core' to 'uclass', meaning U-Boot class. It seems that
this concept relates to a class of drivers (or a subsystem). We shouldn't
- Implemented a GPIO system, trying to keep it simple
-Things to punt for later
-------------------------
+Pre-Relocation Support
+----------------------
+
+For pre-relocation we simply call the driver model init function. Only
+drivers marked with DM_FLAG_PRE_RELOC or the device tree
+'u-boot,dm-pre-reloc' flag are initialised prior to relocation. This helps
+to reduce the driver model overhead.
+
+Then post relocation we throw that away and re-init driver model again.
+For drivers which require some sort of continuity between pre- and
+post-relocation devices, we can provide access to the pre-relocation
+device pointers, but this is not currently implemented (the root device
+pointer is saved but not made available through the driver model API).
-- SPL support - this will have to be present before many drivers can be
-converted, but it seems like we can add it once we are happy with the
-core implementation.
-- Pre-relocation support - similar story
-That is not to say that no thinking has gone into these - in fact there
-is quite a lot there. However, getting these right is non-trivial and
-there is a high cost associated with going down the wrong path.
+SPL Support
+-----------
+
+Driver model can operate in SPL. Its efficient implementation and small code
+size provide for a small overhead which is acceptable for all but the most
+constrained systems.
-For SPL, it may be possible to fit in a simplified driver model with only
-bind and probe methods, to reduce size.
+To enable driver model in SPL, define CONFIG_SPL_DM. You might want to
+consider the following option also. See the main README for more details.
-For pre-relocation we can simply call the driver model init function. Then
-post relocation we throw that away and re-init driver model again. For drivers
-which require some sort of continuity between pre- and post-relocation
-devices, we can provide access to the pre-relocation device pointers.
+ - CONFIG_SYS_MALLOC_SIMPLE
+ - CONFIG_DM_WARN
+ - CONFIG_DM_DEVICE_REMOVE
+ - CONFIG_DM_STDIO
+
+
+Enabling Driver Model
+---------------------
+
+Driver model is being brought into U-Boot gradually. As each subsystems gets
+support, a uclass is created and a CONFIG to enable use of driver model for
+that subsystem.
+
+For example CONFIG_DM_SERIAL enables driver model for serial. With that
+defined, the old serial support is not enabled, and your serial driver must
+conform to driver model. With that undefined, the old serial support is
+enabled and driver model is not available for serial. This means that when
+you convert a driver, you must either convert all its boards, or provide for
+the driver to be compiled both with and without driver model (generally this
+is not very hard).
+
+See the main README for full details of the available driver model CONFIG
+options.
+
+
+Things to punt for later
+------------------------
Uclasses are statically numbered at compile time. It would be possible to
change this to dynamic numbering, but then we would require some sort of
projects / karo-tx-uboot.git / blobdiff