diff options
Diffstat (limited to 'Documentation/DocBook/media/v4l/vidioc-streamon.xml')
| -rw-r--r-- | Documentation/DocBook/media/v4l/vidioc-streamon.xml | 28 |
1 files changed, 22 insertions, 6 deletions
diff --git a/Documentation/DocBook/media/v4l/vidioc-streamon.xml b/Documentation/DocBook/media/v4l/vidioc-streamon.xml index 65dff55079d..df2c63d07ba 100644 --- a/Documentation/DocBook/media/v4l/vidioc-streamon.xml +++ b/Documentation/DocBook/media/v4l/vidioc-streamon.xml @@ -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> |