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media: vidioc-enum-fmt.rst: clarify format preference

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It has been decided to use the ENUM_FMT index value
as a hint for driver preference. This is defined purposedly
in a very liberal way, letting drivers define what "preference"
means.

For instance, the Hantro VPU driver indicates additional
processing to output a given format, and thus implicates
more CPU usage, which is enumerated after native (non-processed)
formats.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
This commit is contained in:
Ezequiel Garcia 2019-12-05 15:24:40 +01:00 committed by Mauro Carvalho Chehab
parent 961f97ab1e
commit 0fb36893c6
1 changed files with 3 additions and 1 deletions
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Documentation/media/uapi/v4l/vidioc-enum-fmt.rst
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@ -44,7 +44,9 @@ To enumerate image formats applications initialize the ``type`` and
the :ref:`VIDIOC_ENUM_FMT` ioctl with a pointer to this structure. Drivers
fill the rest of the structure or return an ``EINVAL`` error code. All
formats are enumerable by beginning at index zero and incrementing by
one until ``EINVAL`` is returned.
one until ``EINVAL`` is returned. If applicable, drivers shall return
formats in preference order, where preferred formats are returned before
(that is, with lower ``index`` value) less-preferred formats.
.. note::