Media Controller
~~~~~~~~~~~~~~~~
-
-The media controller userspace API is documented in DocBook format in
-Documentation/DocBook/media/v4l/media-controller.xml. This document focus
+The media controller userspace API is documented in
+:ref:`the Media Controller uAPI book <media_common>`. This document focus
on the kernel-side implementation of the media framework.
Abstract media device model
Media device
^^^^^^^^^^^^
-A media device is represented by a struct &media_device instance, defined in
-include/media/media-device.h. Allocation of the structure is handled by the
-media device driver, usually by embedding the &media_device instance in a
-larger driver-specific structure.
+A media device is represented by a :c:type:`struct media_device <media_device>`
+instance, defined in ``include/media/media-device.h``.
+Allocation of the structure is handled by the media device driver, usually by
+embedding the :c:type:`media_device` instance in a larger driver-specific
+structure.
Drivers register media device instances by calling
-__media_device_register() via the macro media_device_register()
-and unregistered by calling
-media_device_unregister().
+:cpp:func:`__media_device_register()` via the macro ``media_device_register()``
+and unregistered by calling :cpp:func:`media_device_unregister()`.
Entities
^^^^^^^^
-Entities are represented by a struct &media_entity instance, defined in
-include/media/media-entity.h. The structure is usually embedded into a
-higher-level structure, such as a v4l2_subdev or video_device instance,
-although drivers can allocate entities directly.
+Entities are represented by a :c:type:`struct media_entity <media_entity>`
+instance, defined in ``include/media/media-entity.h``. The structure is usually
+embedded into a higher-level structure, such as
+:ref:`v4l2_subdev` or :ref:`video_device`
+instances, although drivers can allocate entities directly.
Drivers initialize entity pads by calling
-media_entity_pads_init().
+:cpp:func:`media_entity_pads_init()`.
Drivers register entities with a media device by calling
-media_device_register_entity()
+:cpp:func:`media_device_register_entity()`
and unregistred by calling
-media_device_unregister_entity().
+:cpp:func:`media_device_unregister_entity()`.
Interfaces
^^^^^^^^^^
-Interfaces are represented by a struct &media_interface instance, defined in
-include/media/media-entity.h. Currently, only one type of interface is
-defined: a device node. Such interfaces are represented by a struct
-&media_intf_devnode.
+Interfaces are represented by a
+:c:type:`struct media_interface <media_interface>` instance, defined in
+``include/media/media-entity.h``. Currently, only one type of interface is
+defined: a device node. Such interfaces are represented by a
+:c:type:`struct media_intf_devnode <media_intf_devnode>`.
Drivers initialize and create device node interfaces by calling
-media_devnode_create()
+:cpp:func:`media_devnode_create()`
and remove them by calling:
-media_devnode_remove().
+:cpp:func:`media_devnode_remove()`.
Pads
^^^^
-Pads are represented by a struct &media_pad instance, defined in
-include/media/media-entity.h. Each entity stores its pads in a pads array
-managed by the entity driver. Drivers usually embed the array in a
-driver-specific structure.
+Pads are represented by a :c:type:`struct media_pad <media_pad>` instance,
+defined in ``include/media/media-entity.h``. Each entity stores its pads in
+a pads array managed by the entity driver. Drivers usually embed the array in
+a driver-specific structure.
Pads are identified by their entity and their 0-based index in the pads
array.
-Both information are stored in the &media_pad structure, making the
-&media_pad pointer the canonical way to store and pass link references.
+
+Both information are stored in the :c:type:`struct media_pad`, making the
+:c:type:`media_pad` pointer the canonical way to store and pass link references.
Pads have flags that describe the pad capabilities and state.
-%MEDIA_PAD_FL_SINK indicates that the pad supports sinking data.
-%MEDIA_PAD_FL_SOURCE indicates that the pad supports sourcing data.
+``MEDIA_PAD_FL_SINK`` indicates that the pad supports sinking data.
+``MEDIA_PAD_FL_SOURCE`` indicates that the pad supports sourcing data.
+
+.. note::
-NOTE: One and only one of %MEDIA_PAD_FL_SINK and %MEDIA_PAD_FL_SOURCE must
-be set for each pad.
+ One and only one of ``MEDIA_PAD_FL_SINK`` or ``MEDIA_PAD_FL_SOURCE`` must
+ be set for each pad.
Links
^^^^^
-Links are represented by a struct &media_link instance, defined in
-include/media/media-entity.h. There are two types of links:
+Links are represented by a :c:type:`struct media_link <media_link>` instance,
+defined in ``include/media/media-entity.h``. There are two types of links:
-1. pad to pad links:
+**1. pad to pad links**:
Associate two entities via their PADs. Each entity has a list that points
to all links originating at or targeting any of its pads.
the target entity.
Drivers create pad to pad links by calling:
-media_create_pad_link() and remove with media_entity_remove_links().
+:cpp:func:`media_create_pad_link()` and remove with
+:cpp:func:`media_entity_remove_links()`.
-2. interface to entity links:
+**2. interface to entity links**:
Associate one interface to a Link.
Drivers create interface to entity links by calling:
-media_create_intf_link() and remove with media_remove_intf_links().
+:cpp:func:`media_create_intf_link()` and remove with
+:cpp:func:`media_remove_intf_links()`.
.. note::
Links can only be created after having both ends already created.
Links have flags that describe the link capabilities and state. The
-valid values are described at media_create_pad_link() and
-media_create_intf_link().
+valid values are described at :cpp:func:`media_create_pad_link()` and
+:cpp:func:`media_create_intf_link()`.
Graph traversal
^^^^^^^^^^^^^^^
To iterate over all entities belonging to a media device, drivers can use
the media_device_for_each_entity macro, defined in
-include/media/media-device.h.
+``include/media/media-device.h``.
+
+.. code-block:: c
-struct media_entity *entity;
+ struct media_entity *entity;
-media_device_for_each_entity(entity, mdev) {
-// entity will point to each entity in turn
-...
-}
+ media_device_for_each_entity(entity, mdev) {
+ // entity will point to each entity in turn
+ ...
+ }
Drivers might also need to iterate over all entities in a graph that can be
reached only through enabled links starting at a given entity. The media
framework provides a depth-first graph traversal API for that purpose.
-Note that graphs with cycles (whether directed or undirected) are *NOT*
-supported by the graph traversal API. To prevent infinite loops, the graph
-traversal code limits the maximum depth to MEDIA_ENTITY_ENUM_MAX_DEPTH,
-currently defined as 16.
+.. note::
+
+ Graphs with cycles (whether directed or undirected) are **NOT**
+ supported by the graph traversal API. To prevent infinite loops, the graph
+ traversal code limits the maximum depth to ``MEDIA_ENTITY_ENUM_MAX_DEPTH``,
+ currently defined as 16.
Drivers initiate a graph traversal by calling
-media_entity_graph_walk_start()
+:cpp:func:`media_entity_graph_walk_start()`
The graph structure, provided by the caller, is initialized to start graph
traversal at the given entity.
Drivers can then retrieve the next entity by calling
-media_entity_graph_walk_next()
+:cpp:func:`media_entity_graph_walk_next()`
-When the graph traversal is complete the function will return NULL.
+When the graph traversal is complete the function will return ``NULL``.
Graph traversal can be interrupted at any moment. No cleanup function call
is required and the graph structure can be freed normally.
Helper functions can be used to find a link between two given pads, or a pad
connected to another pad through an enabled link
-media_entity_find_link() and media_entity_remote_pad()
+:cpp:func:`media_entity_find_link()` and
+:cpp:func:`media_entity_remote_pad()`.
Use count and power handling
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Due to the wide differences between drivers regarding power management
needs, the media controller does not implement power management. However,
-the &media_entity structure includes a use_count field that media drivers
+the :c:type:`struct media_entity <media_entity>` includes a ``use_count``
+field that media drivers
can use to track the number of users of every entity for power management
needs.
-The &media_entity.@use_count field is owned by media drivers and must not be
+The :c:type:`media_entity<media_entity>`.\ ``use_count`` field is owned by
+media drivers and must not be
touched by entity drivers. Access to the field must be protected by the
-&media_device.@graph_mutex lock.
+:c:type:`media_device`.\ ``graph_mutex`` lock.
Links setup
^^^^^^^^^^^
Link properties can be modified at runtime by calling
-media_entity_setup_link()
+:cpp:func:`media_entity_setup_link()`.
Pipelines and media streams
^^^^^^^^^^^^^^^^^^^^^^^^^^^
When starting streaming, drivers must notify all entities in the pipeline to
prevent link states from being modified during streaming by calling
-media_entity_pipeline_start().
+:cpp:func:`media_entity_pipeline_start()`.
The function will mark all entities connected to the given entity through
enabled links, either directly or indirectly, as streaming.
-The &media_pipeline instance pointed to by the pipe argument will be stored
-in every entity in the pipeline. Drivers should embed the &media_pipeline
-structure in higher-level pipeline structures and can then access the
-pipeline through the &media_entity pipe field.
+The :c:type:`struct media_pipeline <media_pipeline>` instance pointed to by
+the pipe argument will be stored in every entity in the pipeline.
+Drivers should embed the :c:type:`struct media_pipeline <media_pipeline>`
+in higher-level pipeline structures and can then access the
+pipeline through the :c:type:`struct media_entity <media_entity>`
+pipe field.
-Calls to media_entity_pipeline_start() can be nested. The pipeline pointer
-must be identical for all nested calls to the function.
+Calls to :cpp:func:`media_entity_pipeline_start()` can be nested.
+The pipeline pointer must be identical for all nested calls to the function.
-media_entity_pipeline_start() may return an error. In that case, it will
-clean up any of the changes it did by itself.
+:cpp:func:`media_entity_pipeline_start()` may return an error. In that case,
+it will clean up any of the changes it did by itself.
When stopping the stream, drivers must notify the entities with
-media_entity_pipeline_stop().
+:cpp:func:`media_entity_pipeline_stop()`.
-If multiple calls to media_entity_pipeline_start() have been made the same
-number of media_entity_pipeline_stop() calls are required to stop streaming.
-The &media_entity pipe field is reset to NULL on the last nested stop call.
+If multiple calls to :cpp:func:`media_entity_pipeline_start()` have been
+made the same number of :cpp:func:`media_entity_pipeline_stop()` calls
+are required to stop streaming.
+The :c:type:`media_entity`.\ ``pipe`` field is reset to ``NULL`` on the last
+nested stop call.
-Link configuration will fail with -%EBUSY by default if either end of the
+Link configuration will fail with ``-EBUSY`` by default if either end of the
link is a streaming entity. Links that can be modified while streaming must
-be marked with the %MEDIA_LNK_FL_DYNAMIC flag.
+be marked with the ``MEDIA_LNK_FL_DYNAMIC`` flag.
If other operations need to be disallowed on streaming entities (such as
changing entities configuration parameters) drivers can explicitly check the
Link validation
^^^^^^^^^^^^^^^
-Link validation is performed by media_entity_pipeline_start() for any
-entity which has sink pads in the pipeline. The
-&media_entity.@link_validate() callback is used for that purpose. In
-@link_validate() callback, entity driver should check that the properties of
-the source pad of the connected entity and its own sink pad match. It is up
-to the type of the entity (and in the end, the properties of the hardware)
-what matching actually means.
+Link validation is performed by :cpp:func:`media_entity_pipeline_start()`
+for any entity which has sink pads in the pipeline. The
+:c:type:`media_entity`.\ ``link_validate()`` callback is used for that
+purpose. In ``link_validate()`` callback, entity driver should check
+that the properties of the source pad of the connected entity and its own
+sink pad match. It is up to the type of the entity (and in the end, the
+properties of the hardware) what matching actually means.
Subsystems should facilitate link validation by providing subsystem specific
helper functions to provide easy access for commonly needed information, and
.. kernel-doc:: include/media/media-entity.h
+
+
+.. kernel-doc:: include/media/media-device.h
+ :export: drivers/media/media-device.c
+
+.. kernel-doc:: include/media/media-entity.h
+ :export: drivers/media/media-entity.c
int top;
};
-/*
+/**
* struct media_pipeline - Media pipeline related information
*
* @streaming_count: Streaming start count - streaming stop count
* view. The media_entity_pipeline_start() function
* validates all links by calling this operation. Optional.
*
- * Note: Those these callbacks are called with struct media_device.@graph_mutex
+ * .. note:: Those these callbacks are called with struct media_device.@graph_mutex
* mutex held.
*/
struct media_entity_operations {
* @flags: Link flags, as defined in include/uapi/linux/media.h.
*
* Valid values for flags:
- * A %MEDIA_LNK_FL_ENABLED flag indicates that the link is enabled and can be
- * used to transfer media data. When two or more links target a sink pad,
- * only one of them can be enabled at a time.
*
- * A %MEDIA_LNK_FL_IMMUTABLE flag indicates that the link enabled state can't
- * be modified at runtime. If %MEDIA_LNK_FL_IMMUTABLE is set, then
- * %MEDIA_LNK_FL_ENABLED must also be set since an immutable link is
- * always enabled.
+ * - A %MEDIA_LNK_FL_ENABLED flag indicates that the link is enabled and can
+ * be used to transfer media data. When two or more links target a sink pad,
+ * only one of them can be enabled at a time.
+ *
+ * - A %MEDIA_LNK_FL_IMMUTABLE flag indicates that the link enabled state can't
+ * be modified at runtime. If %MEDIA_LNK_FL_IMMUTABLE is set, then
+ * %MEDIA_LNK_FL_ENABLED must also be set since an immutable link is
+ * always enabled.
*
- * NOTE:
+ * .. note::
*
- * Before calling this function, media_entity_pads_init() and
- * media_device_register_entity() should be called previously for both ends.
+ * Before calling this function, media_entity_pads_init() and
+ * media_device_register_entity() should be called previously for both ends.
*/
__must_check int media_create_pad_link(struct media_entity *source,
u16 source_pad, struct media_entity *sink,
* and @sink are NULL.
*
* Valid values for flags:
+ *
* A %MEDIA_LNK_FL_ENABLED flag indicates that the link is enabled and can be
* used to transfer media data. If multiple links are created and this
* flag is passed as an argument, only the first created link will have
*
* @entity: pointer to &media_entity
*
- * Note: this is called automatically when an entity is unregistered via
- * media_device_register_entity().
+ * .. note::
+ *
+ * This is called automatically when an entity is unregistered via
+ * media_device_register_entity().
*/
void media_entity_remove_links(struct media_entity *entity);
* being enabled, the link_setup operation must return -EBUSY and can't
* implicitly disable the first enabled link.
*
- * NOTE: the valid values of the flags for the link is the same as described
- * on media_create_pad_link(), for pad to pad links or the same as described
- * on media_create_intf_link(), for interface to entity links.
+ * .. note::
+ *
+ * The valid values of the flags for the link is the same as described
+ * on media_create_pad_link(), for pad to pad links or the same as described
+ * on media_create_intf_link(), for interface to entity links.
*/
int media_entity_setup_link(struct media_link *link, u32 flags);
* @entity: Starting entity
* @pipe: Media pipeline to be assigned to all entities in the pipeline.
*
- * Note: This is the non-locking version of media_entity_pipeline_start()
+ * ..note:: This is the non-locking version of media_entity_pipeline_start()
*/
__must_check int __media_entity_pipeline_start(struct media_entity *entity,
struct media_pipeline *pipe);
*
* @entity: Starting entity
*
- * Note: This is the non-locking version of media_entity_pipeline_stop()
+ * .. note:: This is the non-locking version of media_entity_pipeline_stop()
*/
void __media_entity_pipeline_stop(struct media_entity *entity);
*
*
* Valid values for flags:
- * The %MEDIA_LNK_FL_ENABLED flag indicates that the interface is connected to
- * the entity hardware. That's the default value for interfaces. An
- * interface may be disabled if the hardware is busy due to the usage
- * of some other interface that it is currently controlling the hardware.
- * A typical example is an hybrid TV device that handle only one type of
- * stream on a given time. So, when the digital TV is streaming,
- * the V4L2 interfaces won't be enabled, as such device is not able to
- * also stream analog TV or radio.
*
- * Note:
+ * - The %MEDIA_LNK_FL_ENABLED flag indicates that the interface is connected to
+ * the entity hardware. That's the default value for interfaces. An
+ * interface may be disabled if the hardware is busy due to the usage
+ * of some other interface that it is currently controlling the hardware.
+ * A typical example is an hybrid TV device that handle only one type of
+ * stream on a given time. So, when the digital TV is streaming,
+ * the V4L2 interfaces won't be enabled, as such device is not able to
+ * also stream analog TV or radio.
+ *
+ * .. note::
*
- * Before calling this function, media_devnode_create() should be called for
- * the interface and media_device_register_entity() should be called for the
- * interface that will be part of the link.
+ * Before calling this function, media_devnode_create() should be called for
+ * the interface and media_device_register_entity() should be called for the
+ * interface that will be part of the link.
*/
__must_check media_create_intf_link(struct media_entity *entity,
struct media_interface *intf,
*
* @link: pointer to &media_link.
*
- * Note: this is an unlocked version of media_remove_intf_link()
+ * .. note:: This is an unlocked version of media_remove_intf_link()
*/
void __media_remove_intf_link(struct media_link *link);
*
* @link: pointer to &media_link.
*
- * Note: prefer to use this one, instead of __media_remove_intf_link()
+ * .. note:: Prefer to use this one, instead of __media_remove_intf_link()
*/
void media_remove_intf_link(struct media_link *link);
*
* @intf: pointer to &media_interface
*
- * Note: this is an unlocked version of media_remove_intf_links().
+ * .. note:: This is an unlocked version of media_remove_intf_links().
*/
void __media_remove_intf_links(struct media_interface *intf);
*
* @intf: pointer to &media_interface
*
- * Notes:
+ * ..note::
*
- * this is called automatically when an entity is unregistered via
- * media_device_register_entity() and by media_devnode_remove().
+ * - This is called automatically when an entity is unregistered via
+ * media_device_register_entity() and by media_devnode_remove().
*
- * Prefer to use this one, instead of __media_remove_intf_links().
+ * - Prefer to use this one, instead of __media_remove_intf_links().
*/
void media_remove_intf_links(struct media_interface *intf);
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