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authorHans Verkuil <hans.verkuil@cisco.com>2017-04-10 16:17:06 -0300
committerMauro Carvalho Chehab <mchehab@s-opensource.com>2017-04-14 22:55:32 -0300
commitaacfed858fcafe888dccc6cbc6ce378a7488c6c7 (patch)
tree7906f7420ed9c1fab185f21922863039bf7048dc /Documentation/media
parentc0e681f5b08a9659202d835d901b59ff1efa919e (diff)
downloadlinux-aacfed858fcafe888dccc6cbc6ce378a7488c6c7.tar.bz2
[media] buffer.rst: clarify how V4L2_CTRL_FLAG_MODIFY_LAYOUT/GRABBER are used
Explain when the V4L2_CTRL_FLAG_MODIFY_LAYOUT and V4L2_CTRL_FLAG_MODIFY_GRABBER flags should be used. Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Diffstat (limited to 'Documentation/media')
-rw-r--r--Documentation/media/uapi/v4l/buffer.rst17
1 files changed, 13 insertions, 4 deletions
diff --git a/Documentation/media/uapi/v4l/buffer.rst b/Documentation/media/uapi/v4l/buffer.rst
index 64613d935edd..ae6ee73f151c 100644
--- a/Documentation/media/uapi/v4l/buffer.rst
+++ b/Documentation/media/uapi/v4l/buffer.rst
@@ -48,10 +48,16 @@ The set of information needed to interpret the content of a buffer (e.g. the
pixel format, the line stride, the tiling orientation or the rotation) is
collectively referred to in the rest of this section as the buffer layout.
+Controls that can modify the buffer layout shall set the
+``V4L2_CTRL_FLAG_MODIFY_LAYOUT`` flag.
+
Modifying formats or controls that influence the buffer size or layout require
the stream to be stopped. Any attempt at such a modification while the stream
is active shall cause the ioctl setting the format or the control to return
-the ``EBUSY`` error code.
+the ``EBUSY`` error code. In that case drivers shall also set the
+``V4L2_CTRL_FLAG_GRABBED`` flag when calling
+:c:func:`VIDIOC_QUERYCTRL` or :c:func:`VIDIOC_QUERY_EXT_CTRL` for such a
+control while the stream is active.
.. note::
@@ -67,7 +73,8 @@ the ``EBUSY`` error code.
Controls that only influence the buffer layout can be modified at any time
when the stream is stopped. As they don't influence the buffer size, no
special handling is needed to synchronize those controls with buffer
-allocation.
+allocation and the ``V4L2_CTRL_FLAG_GRABBED`` flag is cleared once the
+stream is stopped.
Formats and controls that influence the buffer size interact with buffer
allocation. The simplest way to handle this is for drivers to always require
@@ -75,8 +82,10 @@ buffers to be reallocated in order to change those formats or controls. In
that case, to perform such changes, userspace applications shall first stop
the video stream with the :c:func:`VIDIOC_STREAMOFF` ioctl if it is running
and free all buffers with the :c:func:`VIDIOC_REQBUFS` ioctl if they are
-allocated. The format or controls can then be modified, and buffers shall then
-be reallocated and the stream restarted. A typical ioctl sequence is
+allocated. After freeing all buffers the ``V4L2_CTRL_FLAG_GRABBED`` flag
+for controls is cleared. The format or controls can then be modified, and
+buffers shall then be reallocated and the stream restarted. A typical ioctl
+sequence is
#. VIDIOC_STREAMOFF
#. VIDIOC_REQBUFS(0)