media: vb2: reorder checks in vb2_poll()

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When reaching the end of stream, V4L2 clients may expect the
V4L2_EOS_EVENT before being able to dequeue the last buffer, which has
the V4L2_BUF_FLAG_LAST flag set.

If the vb2_poll() function first checks for events and afterwards if
buffers are available, a driver can queue the V4L2_EOS_EVENT event and
return the buffer after the check for events but before the check for
buffers. This causes vb2_poll() to signal that the buffer with
V4L2_BUF_FLAG_LAST can be read without the V4L2_EOS_EVENT being
available.

First, check for available buffers and afterwards for events to ensure
that if vb2_poll() signals POLLIN | POLLRDNORM for the
V4L2_BUF_FLAG_LAST buffer, it also signals POLLPRI for the
V4L2_EOS_EVENT.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

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Michael Tretter 2019-06-27 08:44:32 -04:00 • committed by Mauro Carvalho Chehab

parent 43266ad2b4

commit 8d86a15649

1 changed files with 5 additions and 3 deletions

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drivers/media/common/videobuf2/videobuf2-v4l2.c

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