[PATCH v5 1/5] [media] DocBook media: document mem2mem draining flow

[Philipp Zabel <p.zabel@pengutronix.de>]

Document the interaction between VIDIOC_DECODER_CMD V4L2_DEC_CMD_STOP and
VIDIOC_ENCODER_CMD V4L2_ENC_CMD_STOP to start the draining, the V4L2_EVENT_EOS
event signalling all capture buffers are finished and ready to be dequeud,
the new V4L2_BUF_FLAG_LAST buffer flag indicating the last buffer being dequeued
from the capture queue, and the poll and VIDIOC_DQBUF ioctl return values once
the queue is drained.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
---
Changes since v4:
 - Split out documentation changes into a separate patch
 - Changed wording following Pawel's suggestions.
---
 Documentation/DocBook/media/v4l/io.xml                 | 10 ++++++++++
 Documentation/DocBook/media/v4l/vidioc-decoder-cmd.xml |  9 ++++++++-
 Documentation/DocBook/media/v4l/vidioc-encoder-cmd.xml |  8 +++++++-
 Documentation/DocBook/media/v4l/vidioc-qbuf.xml        |  8 ++++++++
 4 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/Documentation/DocBook/media/v4l/io.xml b/Documentation/DocBook/media/v4l/io.xml
index 1c17f80..f561037 100644
--- a/Documentation/DocBook/media/v4l/io.xml
+++ b/Documentation/DocBook/media/v4l/io.xml
@@ -1129,6 +1129,16 @@ in this buffer has not been created by the CPU but by some DMA-capable unit,
 in which case caches have not been used.</entry>
 	  </row>
 	  <row>
+	    <entry><constant>V4L2_BUF_FLAG_LAST</constant></entry>
+	    <entry>0x00100000</entry>
+	    <entry>Last buffer produced by the hardware. mem2mem codec drivers
+set this flag on the capture queue for the last buffer when the
+<link linkend="vidioc-querybuf">VIDIOC_QUERYBUF</link> or
+<link linkend="vidioc-qbuf">VIDIOC_DQBUF</link> ioctl is called. Any subsequent
+call to the <link linkend="vidioc-qbuf">VIDIOC_DQBUF</link> ioctl will not block
+anymore, but return an &EPIPE;.</entry>
+	  </row>
+	  <row>
 	    <entry><constant>V4L2_BUF_FLAG_TIMESTAMP_MASK</constant></entry>
 	    <entry>0x0000e000</entry>
 	    <entry>Mask for timestamp types below. To test the
diff --git a/Documentation/DocBook/media/v4l/vidioc-decoder-cmd.xml b/Documentation/DocBook/media/v4l/vidioc-decoder-cmd.xml
index 9215627..6502d82 100644
--- a/Documentation/DocBook/media/v4l/vidioc-decoder-cmd.xml
+++ b/Documentation/DocBook/media/v4l/vidioc-decoder-cmd.xml
@@ -197,7 +197,14 @@ be muted when playing back at a non-standard speed.
 this command does nothing. This command has two flags:
 if <constant>V4L2_DEC_CMD_STOP_TO_BLACK</constant> is set, then the decoder will
 set the picture to black after it stopped decoding. Otherwise the last image will
-repeat. If <constant>V4L2_DEC_CMD_STOP_IMMEDIATELY</constant> is set, then the decoder
+repeat. mem2mem decoders will stop producing new frames altogether. They will send
+a <constant>V4L2_EVENT_EOS</constant> event when the last frame has been decoded
+and all frames are ready to be dequeued and will set the
+<constant>V4L2_BUF_FLAG_LAST</constant> buffer flag on the last buffer of the
+capture queue to indicate there will be no new buffers produced to dequeue. Once
+this flag was set, the <link linkend="vidioc-qbuf">VIDIOC_DQBUF</link> ioctl
+will not block anymore, but return an &EPIPE;.
+If <constant>V4L2_DEC_CMD_STOP_IMMEDIATELY</constant> is set, then the decoder
 stops immediately (ignoring the <structfield>pts</structfield> value), otherwise it
 will keep decoding until timestamp >= pts or until the last of the pending data from
 its internal buffers was decoded.
diff --git a/Documentation/DocBook/media/v4l/vidioc-encoder-cmd.xml b/Documentation/DocBook/media/v4l/vidioc-encoder-cmd.xml
index 0619ca5..3cdb841 100644
--- a/Documentation/DocBook/media/v4l/vidioc-encoder-cmd.xml
+++ b/Documentation/DocBook/media/v4l/vidioc-encoder-cmd.xml
@@ -129,7 +129,13 @@ this command.</entry>
 encoding will continue until the end of the current <wordasword>Group
 Of Pictures</wordasword>, otherwise encoding will stop immediately.
 When the encoder is already stopped, this command does
-nothing.</entry>
+nothing. mem2mem encoders will send a <constant>V4L2_EVENT_EOS</constant> event
+when the last frame has been decoded and all frames are ready to be dequeued and
+will set the <constant>V4L2_BUF_FLAG_LAST</constant> buffer flag on the last
+buffer of the capture queue to indicate there will be no new buffers produced to
+dequeue. Once this flag was set, the
+<link linkend="vidioc-qbuf">VIDIOC_DQBUF</link> ioctl will not block anymore,
+but return an &EPIPE;.</entry>
 	  </row>
 	  <row>
 	    <entry><constant>V4L2_ENC_CMD_PAUSE</constant></entry>
diff --git a/Documentation/DocBook/media/v4l/vidioc-qbuf.xml b/Documentation/DocBook/media/v4l/vidioc-qbuf.xml
index 3504a7f..6cfc53b 100644
--- a/Documentation/DocBook/media/v4l/vidioc-qbuf.xml
+++ b/Documentation/DocBook/media/v4l/vidioc-qbuf.xml
@@ -186,6 +186,14 @@ In that case the application should be able to safely reuse the buffer and
 continue streaming.
 	</para>
 	</listitem>
+	<term><errorcode>EPIPE</errorcode></term>
+	<listitem>
+	  <para><constant>VIDIOC_DQBUF</constant> returns this on an empty
+capture queue for mem2mem codecs if a buffer with the
+<constant>V4L2_BUF_FLAG_LAST</constant> was already dequeued and no new buffers
+are expected to become available.
+	</para>
+	</listitem>
       </varlistentry>
     </variablelist>
   </refsect1>
-- 
2.1.4