Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 33 insertions, 0 deletions

diff --git a/Documentation/media/uapi/v4l/streaming-par.rst b/Documentation/media/uapi/v4l/streaming-par.rst
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+.. -*- coding: utf-8; mode: rst -*-
+
+.. _streaming-par:
+
+********************
+Streaming Parameters
+********************
+
+Streaming parameters are intended to optimize the video capture process
+as well as I/O. Presently applications can request a high quality
+capture mode with the :ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` ioctl.
+
+The current video standard determines a nominal number of frames per
+second. If less than this number of frames is to be captured or output,
+applications can request frame skipping or duplicating on the driver
+side. This is especially useful when using the
+:ref:`read() <func-read>` or :ref:`write() <func-write>`, which are
+not augmented by timestamps or sequence counters, and to avoid
+unnecessary data copying.
+
+Finally these ioctls can be used to determine the number of buffers used
+internally by a driver in read/write mode. For implications see the
+section discussing the :ref:`read() <func-read>` function.
+
+To get and set the streaming parameters applications call the
+:ref:`VIDIOC_G_PARM <VIDIOC_G_PARM>` and
+:ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` ioctl, respectively. They take
+a pointer to a struct :c:type:`v4l2_streamparm`, which
+contains a union holding separate parameters for input and output
+devices.
+
+These ioctls are optional, drivers need not implement them. If so, they
+return the ``EINVAL`` error code.