[media] v4l: Add timestamp source flags, mask and document them

Some devices do not produce timestamps that correspond to the end of the
frame. The user space should be informed on the matter. This patch achieves
that by adding buffer flags (and a mask) for timestamp sources since more
possible timestamping points are expected than just two.

A three-bit mask is defined (V4L2_BUF_FLAG_TSTAMP_SRC_MASK) and two of the
eight possible values is are defined V4L2_BUF_FLAG_TSTAMP_SRC_EOF for end of
frame (value zero) V4L2_BUF_FLAG_TSTAMP_SRC_SOE for start of exposure (next
value).

Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Acked-by: Kamil Debski <k.debski@samsung.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

1 files changed, 30 insertions, 6 deletions

diff --git a/Documentation/DocBook/media/v4l/io.xml b/Documentation/DocBook/media/v4l/io.xml
index 5a2e97bbc6bf..1e7ea3c2e2ad 100644
--- a/Documentation/DocBook/media/v4l/io.xml
+++ b/Documentation/DocBook/media/v4l/io.xml
@@ -653,12 +653,6 @@ plane, are stored in struct <structname>v4l2_plane</structname> instead.
 In that case, struct <structname>v4l2_buffer</structname> contains an array of
 plane structures.</para>
 
-      <para>For timestamp types that are sampled from the system clock
-(V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC) it is guaranteed that the timestamp is
-taken after the complete frame has been received (or transmitted in
-case of video output devices). For other kinds of
-timestamps this may vary depending on the driver.</para>
-
     <table frame="none" pgwide="1" id="v4l2-buffer">
       <title>struct <structname>v4l2_buffer</structname></title>
       <tgroup cols="4">
@@ -1125,6 +1119,36 @@ in which case caches have not been used.</entry>
 	    <entry>The CAPTURE buffer timestamp has been taken from the
 	    corresponding OUTPUT buffer. This flag applies only to mem2mem devices.</entry>
 	  </row>
+	  <row>
+	    <entry><constant>V4L2_BUF_FLAG_TSTAMP_SRC_MASK</constant></entry>
+	    <entry>0x00070000</entry>
+	    <entry>Mask for timestamp sources below. The timestamp source
+	    defines the point of time the timestamp is taken in relation to
+	    the frame. Logical 'and' operation between the
+	    <structfield>flags</structfield> field and
+	    <constant>V4L2_BUF_FLAG_TSTAMP_SRC_MASK</constant> produces the
+	    value of the timestamp source.</entry>
+	  </row>
+	  <row>
+	    <entry><constant>V4L2_BUF_FLAG_TSTAMP_SRC_EOF</constant></entry>
+	    <entry>0x00000000</entry>
+	    <entry>End Of Frame. The buffer timestamp has been taken
+	    when the last pixel of the frame has been received or the
+	    last pixel of the frame has been transmitted. In practice,
+	    software generated timestamps will typically be read from
+	    the clock a small amount of time after the last pixel has
+	    been received or transmitten, depending on the system and
+	    other activity in it.</entry>
+	  </row>
+	  <row>
+	    <entry><constant>V4L2_BUF_FLAG_TSTAMP_SRC_SOE</constant></entry>
+	    <entry>0x00010000</entry>
+	    <entry>Start Of Exposure. The buffer timestamp has been
+	    taken when the exposure of the frame has begun. This is
+	    only valid for the
+	    <constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant> buffer
+	    type.</entry>
+	  </row>
 	</tbody>
       </tgroup>
     </table>