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[media] DocBook media: update STREAMON/OFF documentation

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Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
This commit is contained in:
Hans Verkuil 2014-03-07 08:40:59 -03:00 committed by Mauro Carvalho Chehab
parent 87185c958d
commit 078c580cb4
1 changed files with 22 additions and 6 deletions
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28
Documentation/DocBook/media/v4l/vidioc-streamon.xml
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@ -52,16 +52,24 @@
<para>The <constant>VIDIOC_STREAMON</constant> and
<constant>VIDIOC_STREAMOFF</constant> ioctl start and stop the capture
or output process during streaming (<link linkend="mmap">memory
mapping</link> or <link linkend="userp">user pointer</link>) I/O.</para>
mapping</link>, <link linkend="userp">user pointer</link> or
<link linkend="dmabuf">DMABUF</link>) I/O.</para>
<para>Specifically the capture hardware is disabled and no input
<para>Capture hardware is disabled and no input
buffers are filled (if there are any empty buffers in the incoming
queue) until <constant>VIDIOC_STREAMON</constant> has been called.
Accordingly the output hardware is disabled, no video signal is
Output hardware is disabled and no video signal is
produced until <constant>VIDIOC_STREAMON</constant> has been called.
The ioctl will succeed when at least one output buffer is in the
incoming queue.</para>
<para>Memory-to-memory devices will not start until
<constant>VIDIOC_STREAMON</constant> has been called for both the capture
and output stream types.</para>
<para>If <constant>VIDIOC_STREAMON</constant> fails then any already
queued buffers will remain queued.</para>
<para>The <constant>VIDIOC_STREAMOFF</constant> ioctl, apart of
aborting or finishing any DMA in progress, unlocks any user pointer
buffers locked in physical memory, and it removes all buffers from the
@ -70,14 +78,22 @@ dequeued yet will be lost, likewise all images enqueued for output but
not transmitted yet. I/O returns to the same state as after calling
&VIDIOC-REQBUFS; and can be restarted accordingly.</para>
<para>If buffers have been queued with &VIDIOC-QBUF; and
<constant>VIDIOC_STREAMOFF</constant> is called without ever having
called <constant>VIDIOC_STREAMON</constant>, then those queued buffers
will also be removed from the incoming queue and all are returned to the
same state as after calling &VIDIOC-REQBUFS; and can be restarted
accordingly.</para>
<para>Both ioctls take a pointer to an integer, the desired buffer or
stream type. This is the same as &v4l2-requestbuffers;
<structfield>type</structfield>.</para>
<para>If <constant>VIDIOC_STREAMON</constant> is called when streaming
is already in progress, or if <constant>VIDIOC_STREAMOFF</constant> is called
when streaming is already stopped, then the ioctl does nothing and 0 is
returned.</para>
when streaming is already stopped, then 0 is returned. Nothing happens in the
case of <constant>VIDIOC_STREAMON</constant>, but <constant>VIDIOC_STREAMOFF</constant>
will return queued buffers to their starting state as mentioned above.</para>
<para>Note that applications can be preempted for unknown periods right
before or after the <constant>VIDIOC_STREAMON</constant> or
@ -93,7 +109,7 @@ synchronize with other events.</para>
<varlistentry>
<term><errorcode>EINVAL</errorcode></term>
<listitem>
<para>The buffer<structfield>type</structfield> is not supported,
<para>The buffer <structfield>type</structfield> is not supported,
or no buffers have been allocated (memory mapping) or enqueued
(output) yet.</para>
</listitem>