[media] doc-rst: split media_drivers.rst into one file per API type

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

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

^^^^^^^^

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

Remote Controller devices

-------------------------

.. kernel-doc:: include/media/rc-core.h

.. kernel-doc:: include/media/lirc_dev.h

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