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Diffstat (limited to 'Documentation/userspace-api/media/v4l/dev-subdev.rst')
| -rw-r--r-- | Documentation/userspace-api/media/v4l/dev-subdev.rst | 91 |
1 files changed, 58 insertions, 33 deletions
diff --git a/Documentation/userspace-api/media/v4l/dev-subdev.rst b/Documentation/userspace-api/media/v4l/dev-subdev.rst index a4f1df7093e8..2530170a56ae 100644 --- a/Documentation/userspace-api/media/v4l/dev-subdev.rst +++ b/Documentation/userspace-api/media/v4l/dev-subdev.rst @@ -1,4 +1,5 @@ .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later +.. c:namespace:: V4L .. _subdev: @@ -506,8 +507,10 @@ source pads. subdev-formats +.. _subdev-routing: + Streams, multiplexed media pads and internal routing ----------------------------------------------------- +==================================================== 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. @@ -527,12 +530,12 @@ 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. +non-multiplexed subdev drivers. However, if the driver at the sink end of a link +does not support streams, then only stream 0 of source end may be captured. +There may be additional limitations specific to the sink device. 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 @@ -552,7 +555,7 @@ 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 @@ -570,8 +573,31 @@ 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. +Device types and routing setup +------------------------------ + +Different kinds of sub-devices have differing behaviour for route activation, +depending on the hardware. In all cases, however, only routes that have the +``V4L2_SUBDEV_STREAM_FL_ACTIVE`` flag set are active. + +Devices generating the streams may allow enabling and disabling some of the +routes or have a fixed routing configuration. If the routes can be disabled, not +declaring the routes (or declaring them without +``V4L2_SUBDEV_STREAM_FL_ACTIVE`` flag set) in ``VIDIOC_SUBDEV_S_ROUTING`` will +disable the routes. ``VIDIOC_SUBDEV_S_ROUTING`` will still return such routes +back to the user in the routes array, with the ``V4L2_SUBDEV_STREAM_FL_ACTIVE`` +flag unset. + +Devices transporting the streams almost always have more configurability with +respect to routing. Typically any route between the sub-device's sink and source +pads is possible, and multiple routes (usually up to certain limited number) may +be active simultaneously. For such devices, no routes are created by the driver +and user-created routes are fully replaced when ``VIDIOC_SUBDEV_S_ROUTING`` is +called on the sub-device. Such newly created routes have the device's default +configuration for format and selection rectangles. + Configuring streams -^^^^^^^^^^^^^^^^^^^ +------------------- 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 @@ -579,23 +605,22 @@ is started. There are three steps in configuring the streams: -1) Set up links. Connect the pads between sub-devices using the :ref:`Media -Controller API <media_controller>` +1. Set up links. Connect the pads between sub-devices using the + :ref:`Media Controller API <media_controller>` -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 formats and selections in the -sub-device to default values. +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 formats and selections in the sub-device to default values. -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. +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 -^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +--------------------------------- A simple example of a multiplexed stream setup might be as follows: @@ -618,11 +643,11 @@ 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. +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 +2. Configure routing .. flat-table:: Bridge routing table :header-rows: 1 @@ -656,14 +681,14 @@ not differ from normal non-multiplexed media controller setup. - V4L2_SUBDEV_ROUTE_FL_ACTIVE - Pixel data stream from Sensor B -3) Configure formats and selections +3. Configure formats and selections -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. + 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 sub-device. + 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 sub-device. |