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+==========
+Media core
+==========
+
+Video2Linux devices
+-------------------
+
+.. kernel-doc:: include/media/tuner.h
+
+.. kernel-doc:: include/media/tuner-types.h
+
+.. kernel-doc:: include/media/tveeprom.h
+
+.. kernel-doc:: include/media/v4l2-async.h
+
+.. kernel-doc:: include/media/v4l2-ctrls.h
+
+.. kernel-doc:: include/media/v4l2-dv-timings.h
+
+.. kernel-doc:: include/media/v4l2-event.h
+
+.. kernel-doc:: include/media/v4l2-flash-led-class.h
+
+.. kernel-doc:: include/media/v4l2-mc.h
+
+.. kernel-doc:: include/media/v4l2-mediabus.h
+
+.. kernel-doc:: include/media/v4l2-mem2mem.h
+
+.. kernel-doc:: include/media/v4l2-of.h
+
+.. kernel-doc:: include/media/v4l2-rect.h
+
+.. kernel-doc:: include/media/v4l2-subdev.h
+
+.. kernel-doc:: include/media/videobuf2-core.h
+
+.. kernel-doc:: include/media/videobuf2-v4l2.h
+
+.. kernel-doc:: include/media/videobuf2-memops.h
+
+
+Digital TV (DVB) devices
+------------------------
+
+Digital TV Common functions
+---------------------------
+
+.. kernel-doc:: drivers/media/dvb-core/dvb_math.h
+
+.. kernel-doc:: drivers/media/dvb-core/dvb_ringbuffer.h
+
+.. kernel-doc:: drivers/media/dvb-core/dvbdev.h
+
+
+Digital TV Frontend kABI
+------------------------
+
+Digital TV Frontend
+~~~~~~~~~~~~~~~~~~~
+
+The Digital TV Frontend kABI defines a driver-internal interface for
+registering low-level, hardware specific driver to a hardware independent
+frontend layer. It is only of interest for Digital TV device driver writers.
+The header file for this API is named dvb_frontend.h and located in
+drivers/media/dvb-core.
+
+Before using the Digital TV frontend core, the bridge driver should attach
+the frontend demod, tuner and SEC devices and call dvb_register_frontend(),
+in order to register the new frontend at the subsystem. At device
+detach/removal, the bridge driver should call dvb_unregister_frontend() to
+remove the frontend from the core and then dvb_frontend_detach() to free the
+memory allocated by the frontend drivers.
+
+The drivers should also call dvb_frontend_suspend() as part of their
+handler for the &device_driver.suspend(), and dvb_frontend_resume() as
+part of their handler for &device_driver.resume().
+
+few other optional functions are provided to handle some special cases.
+
+.. kernel-doc:: drivers/media/dvb-core/dvb_frontend.h
+
+
+Digital TV Demux kABI
+---------------------
+
+Digital TV Demux
+~~~~~~~~~~~~~~~~
+
+The Kernel Digital TV Demux kABI defines a driver-internal interface for
+registering low-level, hardware specific driver to a hardware independent
+demux layer. It is only of interest for Digital TV device driver writers.
+The header file for this kABI is named demux.h and located in
+drivers/media/dvb-core.
+
+The demux kABI should be implemented for each demux in the system. It is
+used to select the TS source of a demux and to manage the demux resources.
+When the demux client allocates a resource via the demux kABI, it receives
+a pointer to the kABI of that resource.
+
+Each demux receives its TS input from a DVB front-end or from memory, as
+set via this demux kABI. In a system with more than one front-end, the kABI
+can be used to select one of the DVB front-ends as a TS source for a demux,
+unless this is fixed in the HW platform.
+
+The demux kABI only controls front-ends regarding to their connections with
+demuxes; the kABI used to set the other front-end parameters, such as
+tuning, are devined via the Digital TV Frontend kABI.
+
+The functions that implement the abstract interface demux should be defined
+static or module private and registered to the Demux core for external
+access. It is not necessary to implement every function in the struct
+&dmx_demux. For example, a demux interface might support Section filtering,
+but not PES filtering. The kABI client is expected to check the value of any
+function pointer before calling the function: the value of NULL means
+that the function is not available.
+
+Whenever the functions of the demux API modify shared data, the
+possibilities of lost update and race condition problems should be
+addressed, e.g. by protecting parts of code with mutexes.
+
+Note that functions called from a bottom half context must not sleep.
+Even a simple memory allocation without using %GFP_ATOMIC can result in a
+kernel thread being put to sleep if swapping is needed. For example, the
+Linux Kernel calls the functions of a network device interface from a
+bottom half context. Thus, if a demux kABI function is called from network
+device code, the function must not sleep.
+
+
+
+Demux Callback API
+------------------
+
+Demux Callback
+~~~~~~~~~~~~~~
+
+This kernel-space API comprises the callback functions that deliver filtered
+data to the demux client. Unlike the other DVB kABIs, these functions are
+provided by the client and called from the demux code.
+
+The function pointers of this abstract interface are not packed into a
+structure as in the other demux APIs, because the callback functions are
+registered and used independent of each other. As an example, it is possible
+for the API client to provide several callback functions for receiving TS
+packets and no callbacks for PES packets or sections.
+
+The functions that implement the callback API need not be re-entrant: when
+a demux driver calls one of these functions, the driver is not allowed to
+call the function again before the original call returns. If a callback is
+triggered by a hardware interrupt, it is recommended to use the Linux
+bottom half mechanism or start a tasklet instead of making the callback
+function call directly from a hardware interrupt.
+
+This mechanism is implemented by dmx_ts_cb() and dmx_section_cb()
+callbacks.
+
+
+.. kernel-doc:: drivers/media/dvb-core/demux.h
+
+
+Digital TV Conditional Access kABI
+----------------------------------
+
+.. kernel-doc:: drivers/media/dvb-core/dvb_ca_en50221.h
+
+
+Remote Controller devices
+-------------------------
+
+.. kernel-doc:: include/media/rc-core.h
+
+.. kernel-doc:: include/media/lirc_dev.h
+
+
+Media Controller devices
+------------------------
+
+Media Controller
+~~~~~~~~~~~~~~~~
+
+
+The media controller userspace API is documented in DocBook format in
+Documentation/DocBook/media/v4l/media-controller.xml. This document focus
+on the kernel-side implementation of the media framework.
+
+* Abstract media device model:
+
+Discovering a device internal topology, and configuring it at runtime, is one
+of the goals of the media framework. To achieve this, hardware devices are
+modelled as an oriented graph of building blocks called entities connected
+through pads.
+
+An entity is a basic media hardware building block. It can correspond to
+a large variety of logical blocks such as physical hardware devices
+(CMOS sensor for instance), logical hardware devices (a building block
+in a System-on-Chip image processing pipeline), DMA channels or physical
+connectors.
+
+A pad is a connection endpoint through which an entity can interact with
+other entities. Data (not restricted to video) produced by an entity
+flows from the entity's output to one or more entity inputs. Pads should
+not be confused with physical pins at chip boundaries.
+
+A link is a point-to-point oriented connection between two pads, either
+on the same entity or on different entities. Data flows from a source
+pad to a sink pad.
+
+
+* 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.
+
+Drivers register media device instances by calling
+__media_device_register() via the macro media_device_register()
+and unregistered by calling
+media_device_unregister().
+
+* Entities, pads and links:
+
+- 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.
+
+Drivers initialize entity pads by calling
+media_entity_pads_init().
+
+Drivers register entities with a media device by calling
+media_device_register_entity()
+and unregistred by calling
+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.
+
+Drivers initialize and create device node interfaces by calling
+media_devnode_create()
+and remove them by calling:
+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 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.
+
+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.
+
+NOTE: One and only one of %MEDIA_PAD_FL_SINK and %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:
+
+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.
+A given link is thus stored twice, once in the source entity and once in
+the target entity.
+
+Drivers create pad to pad links by calling:
+media_create_pad_link() and remove with media_entity_remove_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().
+
+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().
+
+Graph traversal:
+
+The media framework provides APIs to iterate over entities in a graph.
+
+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.
+
+struct media_entity *entity;
+
+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.
+
+Drivers initiate a graph traversal by calling
+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()
+
+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()
+
+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
+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
+touched by entity drivers. Access to the field must be protected by the
+&media_device.@graph_mutex lock.
+
+Links setup:
+
+Link properties can be modified at runtime by calling
+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().
+
+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.
+
+Calls to 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.
+
+When stopping the stream, drivers must notify the entities with
+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.
+
+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.
+
+If other operations need to be disallowed on streaming entities (such as
+changing entities configuration parameters) drivers can explicitly check the
+media_entity stream_count field to find out if an entity is streaming. This
+operation must be done with the media_device graph_mutex held.
+
+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.
+
+Subsystems should facilitate link validation by providing subsystem specific
+helper functions to provide easy access for commonly needed information, and
+in the end provide a way to use driver-specific callbacks.
+
+.. kernel-doc:: include/media/media-device.h
+
+.. kernel-doc:: include/media/media-devnode.h
+
+.. kernel-doc:: include/media/media-entity.h
+