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media: Documentation: media: Update sub-device API intro

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Update the V4L2 sub-device userspace API introduction to provide more
details on why complex devices might want to register devnodes for the
connected subdevices.

Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Suggested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
This commit is contained in:
Jacopo Mondi 2020-05-07 17:12:48 +02:00 committed by Mauro Carvalho Chehab
parent 5b9f8e4ac9
commit 18200e9e24
1 changed files with 7 additions and 2 deletions
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9
Documentation/driver-api/media/v4l2-subdev.rst
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@ -275,8 +275,13 @@ system the .unbind() method is called. All three callbacks are optional.
V4L2 sub-device userspace API
-----------------------------
Beside exposing a kernel API through the :c:type:`v4l2_subdev_ops` structure,
V4L2 sub-devices can also be controlled directly by userspace applications.
Bridge drivers traditionally expose one or multiple video nodes to userspace,
and control subdevices through the :c:type:`v4l2_subdev_ops` operations in
response to video node operations. This hides the complexity of the underlying
hardware from applications. For complex devices, finer-grained control of the
device than what the video nodes offer may be required. In those cases, bridge
drivers that implement :ref:`the media controller API <media_controller>` may
opt for making the subdevice operations directly accessible from userpace.
Device nodes named ``v4l-subdev``\ *X* can be created in ``/dev`` to access
sub-devices directly. If a sub-device supports direct userspace configuration