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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>

authored by

Sakari Ailus and committed by
Hans Verkuil cd2c7545 74491090

+23
+23
Documentation/userspace-api/media/v4l/dev-subdev.rst
··· 572 572 are independent of similar configurations on other streams. This is 573 573 subject to change in the future. 574 574 575 + Device types and routing setup 576 + ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 577 + 578 + Different kinds of sub-devices have differing behaviour for route activation, 579 + depending on the hardware. In all cases, however, only routes that have the 580 + ``V4L2_SUBDEV_STREAM_FL_ACTIVE`` flag set are active. 581 + 582 + Devices generating the streams may allow enabling and disabling some of the 583 + routes or have a fixed routing configuration. If the routes can be disabled, not 584 + declaring the routes (or declaring them without 585 + ``VIDIOC_SUBDEV_STREAM_FL_ACTIVE`` flag set) in ``VIDIOC_SUBDEV_S_ROUTING`` will 586 + disable the routes. ``VIDIOC_SUBDEV_S_ROUTING`` will still return such routes 587 + back to the user in the routes array, with the ``V4L2_SUBDEV_STREAM_FL_ACTIVE`` 588 + flag unset. 589 + 590 + Devices transporting the streams almost always have more configurability with 591 + respect to routing. Typically any route between the sub-device's sink and source 592 + pads is possible, and multiple routes (usually up to certain limited number) may 593 + be active simultaneously. For such devices, no routes are created by the driver 594 + and user-created routes are fully replaced when ``VIDIOC_SUBDEV_S_ROUTING`` is 595 + called on the sub-device. Such newly created routes have the device's default 596 + configuration for format and selection rectangles. 597 + 575 598 Configuring streams 576 599 ^^^^^^^^^^^^^^^^^^^ 577 600