[media] doc-rst: Convert media API to rst

Move the contents of the media section at
DocBooks/DocBook/device-drivers.tmpl to a new ReST book.

For now, the contents is kept as-is. Next patches will fix
the warnings and add cross-references that were removed due to
the conversion.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

6 files changed, 423 insertions, 379 deletions

diff --git a/Documentation/DocBook/device-drivers.tmpl b/Documentation/DocBook/device-drivers.tmpl
index a20a45b45c30..e9f77f2fe27b 100644
--- a/Documentation/DocBook/device-drivers.tmpl
+++ b/Documentation/DocBook/device-drivers.tmpl
@@ -219,64 +219,6 @@ X!Isound/sound_firmware.c
 -->
   </chapter>
 
-  <chapter id="mediadev">
-     <title>Media Devices</title>
-
-     <sect1><title>Video2Linux devices</title>
-!Iinclude/media/tuner.h
-!Iinclude/media/tuner-types.h
-!Iinclude/media/tveeprom.h
-!Iinclude/media/v4l2-async.h
-!Iinclude/media/v4l2-ctrls.h
-!Iinclude/media/v4l2-dv-timings.h
-!Iinclude/media/v4l2-event.h
-!Iinclude/media/v4l2-flash-led-class.h
-!Iinclude/media/v4l2-mc.h
-!Iinclude/media/v4l2-mediabus.h
-!Iinclude/media/v4l2-mem2mem.h
-!Iinclude/media/v4l2-of.h
-!Iinclude/media/v4l2-rect.h
-!Iinclude/media/v4l2-subdev.h
-!Iinclude/media/videobuf2-core.h
-!Iinclude/media/videobuf2-v4l2.h
-!Iinclude/media/videobuf2-memops.h
-     </sect1>
-     <sect1><title>Digital TV (DVB) devices</title>
-	<sect1><title>Digital TV Common functions</title>
-!Idrivers/media/dvb-core/dvb_math.h
-!Idrivers/media/dvb-core/dvb_ringbuffer.h
-!Idrivers/media/dvb-core/dvbdev.h
-	</sect1>
-	<sect1><title>Digital TV Frontend kABI</title>
-!Pdrivers/media/dvb-core/dvb_frontend.h Digital TV Frontend
-!Idrivers/media/dvb-core/dvb_frontend.h
-	</sect1>
-	<sect1><title>Digital TV Demux kABI</title>
-!Pdrivers/media/dvb-core/demux.h Digital TV Demux
-	<sect1><title>Demux Callback API</title>
-!Pdrivers/media/dvb-core/demux.h Demux Callback
-	</sect1>
-!Idrivers/media/dvb-core/demux.h
-	</sect1>
-	<sect1><title>Digital TV Conditional Access kABI</title>
-!Idrivers/media/dvb-core/dvb_ca_en50221.h
-	</sect1>
-     </sect1>
-    <sect1><title>Remote Controller devices</title>
-!Iinclude/media/rc-core.h
-!Iinclude/media/lirc_dev.h
-    </sect1>
-    <sect1><title>Media Controller devices</title>
-!Pinclude/media/media-device.h Media Controller
-!Iinclude/media/media-device.h
-!Iinclude/media/media-devnode.h
-!Iinclude/media/media-entity.h
-    </sect1>
-    <sect1><title>Consumer Electronics Control devices</title>
-!Iinclude/media/cec-edid.h
-    </sect1>
-
-  </chapter>
 
   <chapter id="uart16x50">
      <title>16x50 UART Driver</title>
diff --git a/Documentation/index.rst b/Documentation/index.rst
index ad07716c73f4..a5a100d43f4f 100644
--- a/Documentation/index.rst
+++ b/Documentation/index.rst
@@ -15,6 +15,7 @@ Contents:
 
    kernel-documentation
    media/media_uapi
+   media/media_drivers
 
 Indices and tables
 ==================
diff --git a/Documentation/media/media_drivers.rst b/Documentation/media/media_drivers.rst
new file mode 100644
index 000000000000..722170cb7f40
--- /dev/null
+++ b/Documentation/media/media_drivers.rst
@@ -0,0 +1,414 @@
+==========
+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
+
diff --git a/drivers/media/dvb-core/demux.h b/drivers/media/dvb-core/demux.h
index 6d3b95b8939d..e8f04f8872f8 100644
--- a/drivers/media/dvb-core/demux.h
+++ b/drivers/media/dvb-core/demux.h
@@ -1,6 +1,10 @@
 /*
  * demux.h
  *
+ * The Kernel Digital TV Demux kABI defines a driver-internal interface for
+ * registering low-level, hardware specific driver to a hardware independent
+ * demux layer.
+ *
  * Copyright (c) 2002 Convergence GmbH
  *
  * based on code:
@@ -32,49 +36,6 @@
 #include <linux/time.h>
 #include <linux/dvb/dmx.h>
 
-/**
- * DOC: 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.
- */
-
 /*
  * Common definitions
  */
@@ -231,30 +192,6 @@ struct dmx_section_feed {
 };
 
 /**
- * DOC: 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.
- */
-
-/**
  * typedef dmx_ts_cb - DVB demux TS filter callback function prototype
  *
  * @buffer1:		Pointer to the start of the filtered TS packets.
diff --git a/drivers/media/dvb-core/dvb_frontend.h b/drivers/media/dvb-core/dvb_frontend.h
index 9592573a0b41..8c551174537a 100644
--- a/drivers/media/dvb-core/dvb_frontend.h
+++ b/drivers/media/dvb-core/dvb_frontend.h
@@ -1,6 +1,10 @@
 /*
  * dvb_frontend.h
  *
+ * The Digital TV Frontend kABI defines a driver-internal interface for
+ * registering low-level, hardware specific driver to a hardware independent
+ * frontend layer.
+ *
  * Copyright (C) 2001 convergence integrated media GmbH
  * Copyright (C) 2004 convergence GmbH
  *
@@ -42,29 +46,6 @@
 
 #include "dvbdev.h"
 
-/**
- * DOC: 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().
- *
- * A few other optional functions are provided to handle some special cases.
- */
-
 /*
  * Maximum number of Delivery systems per frontend. It
  * should be smaller or equal to 32
diff --git a/include/media/media-device.h b/include/media/media-device.h
index f743ae2210ee..4605fee0c228 100644
--- a/include/media/media-device.h
+++ b/include/media/media-device.h
@@ -29,237 +29,6 @@
 #include <media/media-devnode.h>
 #include <media/media-entity.h>
 
-/**
- * DOC: 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.
- */
-
 struct ida;
 struct device;