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

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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>
This commit is contained in:
Sakari Ailus 2013-08-25 17:57:03 -03:00 committed by Mauro Carvalho Chehab
parent c57ff79270
commit 872484ce40
4 changed files with 39 additions and 7 deletions
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36
Documentation/DocBook/media/v4l/io.xml
View File

@ -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>

4
drivers/media/v4l2-core/videobuf2-core.c
View File

@ -2227,7 +2227,9 @@ int vb2_queue_init(struct vb2_queue *q)
WARN_ON(!q->io_modes) ||
WARN_ON(!q->ops->queue_setup) ||
WARN_ON(!q->ops->buf_queue) ||
WARN_ON(q->timestamp_flags & ~V4L2_BUF_FLAG_TIMESTAMP_MASK))
WARN_ON(q->timestamp_flags &
~(V4L2_BUF_FLAG_TIMESTAMP_MASK |
V4L2_BUF_FLAG_TSTAMP_SRC_MASK)))
return -EINVAL;
/* Warn that the driver should choose an appropriate timestamp type */

2
include/media/videobuf2-core.h
View File

@ -312,6 +312,8 @@ struct v4l2_fh;
* @buf_struct_size: size of the driver-specific buffer structure;
* "0" indicates the driver doesn't want to use a custom buffer
* structure type, so sizeof(struct vb2_buffer) will is used
* @timestamp_flags: Timestamp flags; V4L2_BUF_FLAGS_TIMESTAMP_* and
* V4L2_BUF_FLAGS_TSTAMP_SRC_*
* @gfp_flags: additional gfp flags used when allocating the buffers.
* Typically this is 0, but it may be e.g. GFP_DMA or __GFP_DMA32
* to force the buffer allocation to a specific memory zone.

4
include/uapi/linux/videodev2.h
View File

@ -700,6 +700,10 @@ struct v4l2_buffer {
#define V4L2_BUF_FLAG_TIMESTAMP_UNKNOWN 0x00000000
#define V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC 0x00002000
#define V4L2_BUF_FLAG_TIMESTAMP_COPY 0x00004000
/* Timestamp sources. */
#define V4L2_BUF_FLAG_TSTAMP_SRC_MASK 0x00070000
#define V4L2_BUF_FLAG_TSTAMP_SRC_EOF 0x00000000
#define V4L2_BUF_FLAG_TSTAMP_SRC_SOE 0x00010000
/**
* struct v4l2_exportbuffer - export of video buffer as DMABUF file descriptor