On 02/20/2014 08:41 PM, Sakari Ailus wrote:
> 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).
Sorry, but I still have two small notes:
> Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxx>
> ---
> since v5:
> - Add a note on software generated timestamp inaccuracy.
>
> Documentation/DocBook/media/v4l/io.xml | 38 +++++++++++++++++++++++++-----
> drivers/media/v4l2-core/videobuf2-core.c | 4 +++-
> include/media/videobuf2-core.h | 2 ++
> include/uapi/linux/videodev2.h | 4 ++++
> 4 files changed, 41 insertions(+), 7 deletions(-)
>
> diff --git a/Documentation/DocBook/media/v4l/io.xml b/Documentation/DocBook/media/v4l/io.xml
> index 46d24b3..22b87bc 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">
> @@ -1119,6 +1113,38 @@ 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, depending on the system and other activity
s/been received/been received or transmitted/
> + 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. In
> + practice, software generated timestamps will typically be
> + read from the clock a small amount of time after the last
> + pixel has been received, depending on the system and other
> + activity in it. This is only valid for buffer type
> + <constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>.</entry>
I would move the last sentence up to just before "In practice...". The
way it is now it looks like an afterthought.
I am also not sure whether the whole "In practice" sentence is valid
here. Certainly the bit about "the last pixel" isn't since this is the
"SOE" case and not the End Of Frame. In the case of the UVC driver (and that's
the only one using this timestamp source) the timestamps come from the
hardware as I understand it, so the "software generated" bit doesn't
apply.
I would actually be inclined to drop it altogether for this particular
timestamp source. But it's up to Laurent.
Regards,
Hans
> + </row>
> </tbody>
> </tgroup>
> </table>
> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
> index 5a5fb7f..6e314b0 100644
> --- a/drivers/media/v4l2-core/videobuf2-core.c
> +++ b/drivers/media/v4l2-core/videobuf2-core.c
> @@ -2195,7 +2195,9 @@ 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_type & ~V4L2_BUF_FLAG_TIMESTAMP_MASK))
> + WARN_ON(q->timestamp_type &
> + ~(V4L2_BUF_FLAG_TIMESTAMP_MASK |
> + V4L2_BUF_FLAG_TSTAMP_SRC_MASK)))
> return -EINVAL;
>
> /* Warn that the driver should choose an appropriate timestamp type */
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index bef53ce..b6b992d 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -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_type: 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.
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index e9ee444..82e8661 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -695,6 +695,10 @@ 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
>
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