Specify that STREAMON/OFF should return 0 if the stream is already
started/stopped.

The spec never specified what the correct behavior is. This ambiguity
was resolved during the 2012 Media Workshop.

Signed-off-by: Hans Verkuil <hans.verk...@cisco.com>
Reviewed-by: Sylwester Nawrocki <s.nawro...@samsung.com>
Acked-by: Laurent Pinchart <laurent.pinch...@ideasonboard.com>
---
 Documentation/DocBook/media/v4l/vidioc-streamon.xml |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/Documentation/DocBook/media/v4l/vidioc-streamon.xml 
b/Documentation/DocBook/media/v4l/vidioc-streamon.xml
index 81cca45..716ea15 100644
--- a/Documentation/DocBook/media/v4l/vidioc-streamon.xml
+++ b/Documentation/DocBook/media/v4l/vidioc-streamon.xml
@@ -74,7 +74,12 @@ not transmitted yet. I/O returns to the same state as after 
calling
 stream type. This is the same as &v4l2-requestbuffers;
 <structfield>type</structfield>.</para>
 
-    <para>Note applications can be preempted for unknown periods right
+    <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>
+
+    <para>Note that applications can be preempted for unknown periods right
 before or after the <constant>VIDIOC_STREAMON</constant> or
 <constant>VIDIOC_STREAMOFF</constant> calls, there is no notion of
 starting or stopping "now". Buffer timestamps can be used to
-- 
1.7.10.4

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