diff --git a/Documentation/driver-api/media/v4l2-subdev.rst b/Documentation/driver-api/media/v4l2-subdev.rst index 6f8d79926aa5..260cfa8c3f3d 100644 --- a/Documentation/driver-api/media/v4l2-subdev.rst +++ b/Documentation/driver-api/media/v4l2-subdev.rst @@ -593,6 +593,14 @@ before calling v4l2_subdev_init_finalize(): This shares the driver's private mutex between the controls and the states. +Streams, multiplexed media pads and internal routing +---------------------------------------------------- + +A subdevice driver can implement support for multiplexed streams by setting +the V4L2_SUBDEV_FL_STREAMS subdev flag and implementing support for +centrally managed subdev active state, routing and stream based +configuration. + V4L2 sub-device functions and data structures --------------------------------------------- diff --git a/Documentation/userspace-api/media/v4l/dev-subdev.rst b/Documentation/userspace-api/media/v4l/dev-subdev.rst index a67c2749089a..7d1b8ebd4e17 100644 --- a/Documentation/userspace-api/media/v4l/dev-subdev.rst +++ b/Documentation/userspace-api/media/v4l/dev-subdev.rst @@ -503,3 +503,141 @@ source pads. :maxdepth: 1 subdev-formats + +Streams, multiplexed media pads and internal routing +---------------------------------------------------- + +Commonly V4L2 subdevices support only separate video streams, that is, only a +single stream can pass through a media link and a media pad. Thus each pad +contains a format configuration for that single stream. In some cases a subdev +can do stream processing and split a stream into two or compose two streams +into one, but the inputs and outputs for the subdev are still a single stream +per pad. + +Some hardware, e.g. MIPI CSI-2, support multiplexed streams, that is, multiple +data streams are transmitted on the same bus, which is represented by a media +link connecting a transmitter source pad with a sink pad on the receiver. For +example, a camera sensor can produce two distinct streams, a pixel stream and a +metadata stream, which are transmitted on the multiplexed data bus, represented +by a media link which connects the single sensor's source pad with the receiver +sink pad. The stream-aware receiver will de-multiplex the streams received on +the its sink pad and allows to route them individually to one of its source +pads. + +Subdevice drivers that support multiplexed streams are compatible with +non-multiplexed subdev drivers, but, of course, require a routing configuration +where the link between those two types of drivers contains only a single +stream. + +Understanding streams +^^^^^^^^^^^^^^^^^^^^^ + +A stream is a stream of content (e.g. pixel data or metadata) flowing through +the media pipeline from a source (e.g. a sensor) towards the final sink (e.g. a +receiver and demultiplexer in a SoC). Each media link carries all the enabled +streams from one end of the link to the other, and subdevices have routing +tables which describe how the incoming streams from sink pads are routed to the +source pads. + +A stream ID (often just "stream") is a media link-local identifier for a stream. +In other words, a particular stream ID must exist on both sides of a media +link, but another stream ID can be used for the same stream at the other side +of the subdevice. + +A stream at a specific point in the media pipeline is identified with the +subdev and a (pad, stream) pair. For subdevices that do not support +multiplexed streams the 'stream' is always 0. + +Configuring streams +^^^^^^^^^^^^^^^^^^^ + +The configuration of the streams is done individually for each subdevice and +the validity of the streams between subdevices is validated when the pipeline +is started. + +There are three steps in configuring the streams: + +1) Set up links. Connect the pads between subdevices using the :ref:`Media +Controller API ` + +2) Routing. The routing table for the subdevice must be set with +:ref:`VIDIOC_SUBDEV_S_ROUTING ` ioctl. Note that +setting the routing table will reset all the stream configurations in a media +entity. + +3) Configure streams. Each route endpoint must be configured +with :ref:`VIDIOC_SUBDEV_S_FMT `. + +Multiplexed streams setup example +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +A simple example of a multiplexed stream setup might be as follows: + +- Two identical sensors (Sensor A and Sensor B). Each sensor has a single source + pad (pad 0) which carries a pixel data stream. + +- Multiplexer bridge (Bridge). The bridge has two sink pads, connected to the + sensors (pads 0, 1), and one source pad (pad 2), which outputs two streams. + +- Receiver in the SoC (Receiver). The receiver has a single sink pad (pad 0), + connected to the bridge, and two source pads (pads 1-2), going to the DMA + engine. The receiver demultiplexes the incoming streams to the source pads. + +- DMA Engines in the SoC (DMA Engine), one for each stream. Each DMA engine is + connected to a single source pad in the receiver. + +The sensors, the bridge and the receiver are modeled as V4L2 subdevices, +exposed to userspace via /dev/v4l-subdevX device nodes. The DMA engines are +modeled as V4L2 devices, exposed to userspace via /dev/videoX nodes. + +To configure this pipeline, the userspace must take the following steps: + +1) Set up media links between entities: connect the sensors to the bridge, +bridge to the receiver, and the receiver to the DMA engines. This step does +not differ from normal non-multiplexed media controller setup. + +2) Configure routing. + +.. flat-table:: Bridge routing table + :header-rows: 1 + + * - Sink Pad/Stream + - Source Pad/Stream + - Routing Flags + - Comments + * - 0/0 + - 2/0 + - V4L2_SUBDEV_ROUTE_FL_ACTIVE + - Pixel data stream from Sensor A + * - 1/0 + - 2/1 + - V4L2_SUBDEV_ROUTE_FL_ACTIVE + - Pixel data stream from Sensor B + +.. flat-table:: Receiver routing table + :header-rows: 1 + + * - Sink Pad/Stream + - Source Pad/Stream + - Routing Flags + - Comments + * - 0/0 + - 1/0 + - V4L2_SUBDEV_ROUTE_FL_ACTIVE + - Pixel data stream from Sensor A + * - 0/1 + - 2/0 + - V4L2_SUBDEV_ROUTE_FL_ACTIVE + - Pixel data stream from Sensor B + +3) Configure streams + +After configuring the routing table, the next step is configuring the streams. +This step is similar to configuring the pads in a non-multiplexed streams +setup, with the difference that we need to configure each (pad, stream) pair +(i.e. route endpoint) instead of just a pad. + +A common way to accomplish this is to start from the sensors and propagate the +configurations along the stream towards the receiver, +using :ref:`VIDIOC_SUBDEV_S_FMT ` ioctls to configure each +stream endpoint in each subdev.