[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>

Documentation/DocBook/media/v4l/compat.xml

@@ -2477,6 +2477,18 @@ that used it. It was originally scheduled for removal in 2.6.35.
       </orderedlist>
     </section>
 
+    <section>
+      <title>V4L2 in Linux 3.9</title>
+      <orderedlist>
+        <listitem>
+	  <para>Added timestamp types to
+	  <structfield>flags</structfield> field in
+	  <structname>v4l2_buffer</structname>. See <xref
+	  linkend="buffer-flags" />.</para>
+        </listitem>
+      </orderedlist>
+    </section>
+
     <section id="other">
       <title>Relation of V4L2 to other Linux multimedia APIs</title>
 

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>

Documentation/DocBook/media/v4l/v4l2.xml

@@ -139,6 +139,16 @@ structs, ioctls) must be noted in more detail in the history chapter
 (compat.xml), along with the possible impact on existing drivers and
 applications. -->
 
+      <revision>
+	<revnumber>3.9</revnumber>
+	<date>2012-12-03</date>
+	<authorinitials>sa</authorinitials>
+	<revremark>Added timestamp types to
+	<structname>v4l2_buffer</structname>, see <xref
+	linkend="buffer-flags" />.
+	</revremark>
+      </revision>
+
       <revision>
 	<revnumber>3.6</revnumber>
 	<date>2012-07-02</date>
@@ -472,7 +482,7 @@ and discussions on the V4L mailing list.</revremark>
 </partinfo>
 
 <title>Video for Linux Two API Specification</title>
- <subtitle>Revision 3.6</subtitle>
+ <subtitle>Revision 3.9</subtitle>
 
   <chapter id="common">
     &sub-common;

include/uapi/linux/videodev2.h

@@ -701,6 +701,10 @@ struct v4l2_buffer {
 /* Cache handling flags */
 #define V4L2_BUF_FLAG_NO_CACHE_INVALIDATE	0x0800
 #define V4L2_BUF_FLAG_NO_CACHE_CLEAN		0x1000
+/* Timestamp type */
+#define V4L2_BUF_FLAG_TIMESTAMP_MASK		0xe000
+#define V4L2_BUF_FLAG_TIMESTAMP_UNKNOWN		0x0000
+#define V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC	0x2000
 
 /**
  * struct v4l2_exportbuffer - export of video buffer as DMABUF file descriptor