On Thu November 15 2012 23:06:44 Sakari Ailus wrote:
> 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.
>
> Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxx>
> Acked-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> ---
> Documentation/DocBook/media/v4l/io.xml | 25 +++++++++++++++++++++++++
> include/uapi/linux/videodev2.h | 4 ++++
> 2 files changed, 29 insertions(+), 0 deletions(-)
>
> diff --git a/Documentation/DocBook/media/v4l/io.xml b/Documentation/DocBook/media/v4l/io.xml
> index 7e2f3d7..d598f2c 100644
> --- a/Documentation/DocBook/media/v4l/io.xml
> +++ b/Documentation/DocBook/media/v4l/io.xml
> @@ -938,6 +938,31 @@ 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.</tt> </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 3.8 and may be either monotonic (see
> + below) or realtime. Monotonic clock has been favoured in
> + embedded systems whereas most of the drivers use the
> + realtime clock.</entry>
Isn't 'wallclock time' a better expression? It is probably a good idea as well
to add the userspace call that gives the same clock: gettimeofday or
clock_gettime(CLOCK_REALTIME) for the wallclock time and clock_gettime(CLOCK_MONOTONIC)
for the monotonic time. That way apps can do the same call and compare it to the
timestamp received.
> + </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 <tt>clock_gettime(2)</tt>
Ah, you mentioned it here already for the monotonic clock :-)
> + .</entry>
> + </row>
> </tbody>
> </tgroup>
> </table>
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 2fff7ff..410ea9f 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -686,6 +686,10 @@ 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
>
> /*
> * O V E R L A Y P R E V I E W
>
Regards,
Hans
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