Some devices such as the uvc produce timestamps at the beginning of the
frame rather than at the end of it. Add a buffer flag
(V4L2_BUF_FLAG_TIMESTAMP_SOF) to tell about this.
Also document timestamp_type in struct vb2_queue, and make the uvc set the
buffer flag.
Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxx>
---
since v4:
- Fixes according to Hans's comments.
- Note in comment the uvc driver will set the SOF flag from now on.
- Change comment of vb2_queue timestamp_type field: this is timestamp flags
rather than just type. I stopped short of renaming the field.
Documentation/DocBook/media/v4l/io.xml | 19 ++++++++++++++-----
drivers/media/usb/uvc/uvc_queue.c | 3 ++-
include/media/videobuf2-core.h | 1 +
include/uapi/linux/videodev2.h | 10 ++++++++++
4 files changed, 27 insertions(+), 6 deletions(-)
diff --git a/Documentation/DocBook/media/v4l/io.xml b/Documentation/DocBook/media/v4l/io.xml
index 2c155cc..3aee210 100644
--- a/Documentation/DocBook/media/v4l/io.xml
+++ b/Documentation/DocBook/media/v4l/io.xml
@@ -654,11 +654,12 @@ 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>
+ <para>The timestamp is taken once the complete frame has been
+received (or transmitted for output devices) unless
+<constant>V4L2_BUF_FLAG_TIMESTAMP_SOF</constant> buffer flag is set.
+If <constant>V4L2_BUF_FLAG_TIMESTAMP_SOF</constant> is set, the
+timestamp is taken when the first pixel of the frame is received
+(or transmitted).</para>
<table frame="none" pgwide="1" id="v4l2-buffer">
<title>struct <structname>v4l2_buffer</structname></title>
@@ -1120,6 +1121,14 @@ 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_TIMESTAMP_SOF</constant></entry>
+ <entry>0x00010000</entry>
+ <entry>The buffer timestamp has been taken when the first
+ pixel is received (or transmitted for output devices). If
+ this flag is not set, the timestamp is taken when the
+ entire frame has been received (or transmitted).</entry>
+ </row>
</tbody>
</tgroup>
</table>
diff --git a/drivers/media/usb/uvc/uvc_queue.c b/drivers/media/usb/uvc/uvc_queue.c
index cd962be..0d80512 100644
--- a/drivers/media/usb/uvc/uvc_queue.c
+++ b/drivers/media/usb/uvc/uvc_queue.c
@@ -149,7 +149,8 @@ int uvc_queue_init(struct uvc_video_queue *queue, enum v4l2_buf_type type,
queue->queue.buf_struct_size = sizeof(struct uvc_buffer);
queue->queue.ops = &uvc_queue_qops;
queue->queue.mem_ops = &vb2_vmalloc_memops;
- queue->queue.timestamp_type = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
+ queue->queue.timestamp_type = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC
+ | V4L2_BUF_FLAG_TIMESTAMP_SOF;
ret = vb2_queue_init(&queue->queue);
if (ret)
return ret;
diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index 6781258..033efc7 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -307,6 +307,7 @@ 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_type: Timestamp flags; V4L2_BUF_FLAGS_TIMESTAMP_*
* @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.
diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
index 691077d..c57765e 100644
--- a/include/uapi/linux/videodev2.h
+++ b/include/uapi/linux/videodev2.h
@@ -695,6 +695,16 @@ 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 taken once the first pixel is received (or transmitted).
+ * If the flag is not set the buffer timestamp is taken at the end of
+ * the frame. This is not a timestamp type.
+ *
+ * In general drivers should not use this flag if the end-of-frame
+ * timestamps is as good quality as the start-of-frame one; the
+ * V4L2_EVENT_FRAME_SYNC event should be used in that case instead.
+ */
+#define V4L2_BUF_FLAG_TIMESTAMP_SOF 0x00010000
/**
* struct v4l2_exportbuffer - export of video buffer as DMABUF file descriptor
--
1.7.10.4
--
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