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media: Documentation: media: Update sub-device API intro
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>
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@ -275,8 +275,13 @@ system the .unbind() method is called. All three callbacks are optional.
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V4L2 sub-device userspace API
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-----------------------------
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Beside exposing a kernel API through the :c:type:`v4l2_subdev_ops` structure,
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V4L2 sub-devices can also be controlled directly by userspace applications.
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Bridge drivers traditionally expose one or multiple video nodes to userspace,
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and control subdevices through the :c:type:`v4l2_subdev_ops` operations in
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response to video node operations. This hides the complexity of the underlying
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hardware from applications. For complex devices, finer-grained control of the
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device than what the video nodes offer may be required. In those cases, bridge
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drivers that implement :ref:`the media controller API <media_controller>` may
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opt for making the subdevice operations directly accessible from userpace.
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Device nodes named ``v4l-subdev``\ *X* can be created in ``/dev`` to access
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sub-devices directly. If a sub-device supports direct userspace configuration
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