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-rw-r--r-- | Documentation/userspace-api/media/v4l/dev-subdev.rst | 84 |
1 files changed, 55 insertions, 29 deletions
diff --git a/Documentation/userspace-api/media/v4l/dev-subdev.rst b/Documentation/userspace-api/media/v4l/dev-subdev.rst index 7d1b8ebd4e17..a4f1df7093e8 100644 --- a/Documentation/userspace-api/media/v4l/dev-subdev.rst +++ b/Documentation/userspace-api/media/v4l/dev-subdev.rst @@ -406,6 +406,8 @@ pixel array is not rectangular but cross-shaped or round. The maximum size may also be smaller than the BOUNDS rectangle. +.. _format-propagation: + Order of configuration and format propagation --------------------------------------------- @@ -507,12 +509,12 @@ source pads. 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. +Simple V4L2 sub-devices do not support multiple, unrelated video streams, +and only a single stream can pass through a media link and a media pad. +Thus each pad contains a format and selection configuration for that +single stream. 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 @@ -535,38 +537,62 @@ 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 +streams from one end of the link to the other, and sub-devices 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 +A stream ID is a media pad-local identifier for a stream. Streams IDs of +the same stream must be equal on both ends of a link. 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. +of the sub-device. + +A stream at a specific point in the media pipeline is identified by the +sub-device and a (pad, stream) pair. For sub-devices that do not support +multiplexed streams the 'stream' field is always 0. + +Interaction between routes, streams, formats and selections +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +The addition of streams to the V4L2 sub-device interface moves the sub-device +formats and selections from pads to (pad, stream) pairs. Besides the +usual pad, also the stream ID needs to be provided for setting formats and +selections. The order of configuring formats and selections along a stream is +the same as without streams (see :ref:`format-propagation`). + +Instead of the sub-device wide merging of streams from all sink pads +towards all source pads, data flows for each route are separate from each +other. Any number of routes from streams on sink pads towards streams on +source pads is allowed, to the extent supported by drivers. For every +stream on a source pad, however, only a single route is allowed. -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. +Any configurations of a stream within a pad, such as format or selections, +are independent of similar configurations on other streams. This is +subject to change in the future. 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 +The configuration of the streams is done individually for each sub-device and +the validity of the streams between sub-devices 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 +1) Set up links. Connect the pads between sub-devices using the :ref:`Media Controller API <media_controller>` -2) Routing. The routing table for the subdevice must be set with +2) Streams. Streams are declared and their routing is configured by +setting the routing table for the sub-device using :ref:`VIDIOC_SUBDEV_S_ROUTING <VIDIOC_SUBDEV_G_ROUTING>` ioctl. Note that -setting the routing table will reset all the stream configurations in a media -entity. +setting the routing table will reset formats and selections in the +sub-device to default values. -3) Configure streams. Each route endpoint must be configured -with :ref:`VIDIOC_SUBDEV_S_FMT <VIDIOC_SUBDEV_G_FMT>`. +3) Configure formats and selections. Formats and selections of each stream +are configured separately as documented for plain sub-devices in +:ref:`format-propagation`. The stream ID is set to the same stream ID +associated with either sink or source pads of routes configured using the +:ref:`VIDIOC_SUBDEV_S_ROUTING <VIDIOC_SUBDEV_G_ROUTING>` ioctl. Multiplexed streams setup example ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ @@ -586,7 +612,7 @@ A simple example of a multiplexed stream setup might be as follows: - 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, +The sensors, the bridge and the receiver are modeled as V4L2 sub-devices, exposed to userspace via /dev/v4l-subdevX device nodes. The DMA engines are modeled as V4L2 devices, exposed to userspace via /dev/videoX nodes. @@ -596,7 +622,7 @@ To configure this pipeline, the userspace must take the following steps: 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. +2) Configure routing .. flat-table:: Bridge routing table :header-rows: 1 @@ -630,14 +656,14 @@ not differ from normal non-multiplexed media controller setup. - V4L2_SUBDEV_ROUTE_FL_ACTIVE - Pixel data stream from Sensor B -3) Configure streams +3) Configure formats and selections -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. +After configuring routing, the next step is configuring the formats and +selections for the streams. This is similar to performing this step without +streams, with just one exception: the ``stream`` field needs to be assigned +to the value of the stream ID. 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 <VIDIOC_SUBDEV_G_FMT>` ioctls to configure each -stream endpoint in each subdev. +stream endpoint in each sub-device. |