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media: Documentation: Document S_ROUTING behaviour 

Document S_ROUTING behaviour for different devices.

Generally in devices that produce streams the streams are static and some
can be enabled and disabled, whereas in devices that just transport them
or write them to memory, more configurability is allowed. Document this.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Julien Massot <julien.massot@collabora.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
This commit is contained in:
Sakari Ailus 2023-09-21 12:12:49 +03:00 committed by Hans Verkuil
parent 744910906d
commit cd2c75454d
1 changed files with 23 additions and 0 deletions
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Documentation/userspace-api/media/v4l/dev-subdev.rst
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@ -572,6 +572,29 @@ 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
``VIDIOC_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
^^^^^^^^^^^^^^^^^^^