[media] v4l: Define video buffer flags for timestamp types

Define video buffer flags for different timestamp types. Everything up to
now have used either realtime clock or monotonic clock, without a way to
tell which clock the timestamp was taken from.
Also document that the clock source of the timestamp in the timestamp field
depends on buffer flags.

[mchehab@redhat.com: fix a few wrong references to Kernel 3.8 - as this patch
 is meant for 3.9]
Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 42 insertions, 11 deletions

diff --git a/Documentation/DocBook/media/v4l/io.xml b/Documentation/DocBook/media/v4l/io.xml
index 388a3403265..09e8dcf5e9c 100644
--- a/Documentation/DocBook/media/v4l/io.xml
+++ b/Documentation/DocBook/media/v4l/io.xml
@@ -741,17 +741,19 @@ applications when an output stream.</entry>
 	    <entry>struct timeval</entry>
 	    <entry><structfield>timestamp</structfield></entry>
 	    <entry></entry>
-	    <entry><para>For input streams this is the
-system time (as returned by the <function>gettimeofday()</function>
-function) when the first data byte was captured. For output streams
-the data will not be displayed before this time, secondary to the
-nominal frame rate determined by the current video standard in
-enqueued order. Applications can for example zero this field to
-display frames as soon as possible. The driver stores the time at
-which the first data byte was actually sent out in the
-<structfield>timestamp</structfield> field. This permits
-applications to monitor the drift between the video and system
-clock.</para></entry>
+	    <entry><para>For input streams this is time when the first data
+	    byte was captured, as returned by the
+	    <function>clock_gettime()</function> function for the relevant
+	    clock id; see <constant>V4L2_BUF_FLAG_TIMESTAMP_*</constant> in
+	    <xref linkend="buffer-flags" />. For output streams the data
+	    will not be displayed before this time, secondary to the nominal
+	    frame rate determined by the current video standard in enqueued
+	    order. Applications can for example zero this field to display
+	    frames as soon as possible. The driver stores the time at which
+	    the first data byte was actually sent out in the
+	    <structfield>timestamp</structfield> field. This permits
+	    applications to monitor the drift between the video and system
+	    clock.</para></entry>
 	  </row>
 	  <row>
 	    <entry>&v4l2-timecode;</entry>
@@ -1114,6 +1116,35 @@ Typically applications shall use this flag for output buffers if the data
 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_TIMESTAMP_MASK</constant></entry>
+	    <entry>0xe000</entry>
+	    <entry>Mask for timestamp types below. To test the
+	    timestamp type, mask out bits not belonging to timestamp
+	    type by performing a logical and operation with buffer
+	    flags and timestamp mask.</entry>
+	  </row>
+	  <row>
+	    <entry><constant>V4L2_BUF_FLAG_TIMESTAMP_UNKNOWN</constant></entry>
+	    <entry>0x0000</entry>
+	    <entry>Unknown timestamp type. This type is used by
+	    drivers before Linux 3.9 and may be either monotonic (see
+	    below) or realtime (wall clock). Monotonic clock has been
+	    favoured in embedded systems whereas most of the drivers
+	    use the realtime clock. Either kinds of timestamps are
+	    available in user space via
+	    <function>clock_gettime(2)</function> using clock IDs
+	    <constant>CLOCK_MONOTONIC</constant> and
+	    <constant>CLOCK_REALTIME</constant>, respectively.</entry>
+	  </row>
+	  <row>
+	    <entry><constant>V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC</constant></entry>
+	    <entry>0x2000</entry>
+	    <entry>The buffer timestamp has been taken from the
+	    <constant>CLOCK_MONOTONIC</constant> clock. To access the
+	    same clock outside V4L2, use
+	    <function>clock_gettime(2)</function> .</entry>
+	  </row>
 	</tbody>
       </tgroup>
     </table>