[media] DocBook media: update STREAMON/OFF documentation

[mirror_ubuntu-bionic-kernel.git] / Documentation / DocBook / media / v4l / vidioc-streamon.xml

diff --git a/Documentation/DocBook/media/v4l/vidioc-streamon.xml b/Documentation/DocBook/media/v4l/vidioc-streamon.xml
index 65dff55079d71763942fc8991ee8ae76a80bc65d..df2c63d07bac8e81b6c90c2b62a31bd62e9ab37f 100644 (file)
--- 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>