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[media] DocBook media: fix the poll() 'no QBUF' documentation 

Clarify what poll() returns if STREAMON was called but not QBUF.
Make explicit the different behavior for this scenario for
capture and output devices.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
This commit is contained in:
Hans Verkuil 2014-09-20 16:16:36 -03:00 committed by Mauro Carvalho Chehab
parent 58d75f4b1c
commit acf92046a0
1 changed files with 10 additions and 2 deletions
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12
Documentation/DocBook/media/v4l/func-poll.xml
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@ -44,10 +44,18 @@ Capture devices set the <constant>POLLIN</constant> and
flags. When the function timed out it returns a value of zero, on
failure it returns <returnvalue>-1</returnvalue> and the
<varname>errno</varname> variable is set appropriately. When the
application did not call &VIDIOC-QBUF; or &VIDIOC-STREAMON; yet the
application did not call &VIDIOC-STREAMON; the
<function>poll()</function> function succeeds, but sets the
<constant>POLLERR</constant> flag in the
<structfield>revents</structfield> field.</para>
<structfield>revents</structfield> field. When the
application has called &VIDIOC-STREAMON; for a capture device but hasn't
yet called &VIDIOC-QBUF;, the <function>poll()</function> function
succeeds and sets the <constant>POLLERR</constant> flag in the
<structfield>revents</structfield> field. For output devices this
same situation will cause <function>poll()</function> to succeed
as well, but it sets the <constant>POLLOUT</constant> and
<constant>POLLWRNORM</constant> flags in the <structfield>revents</structfield>
field.</para>
<para>When use of the <function>read()</function> function has
been negotiated and the driver does not capture yet, the