Hi Hans, On Thursday 20 February 2014 21:36:51 Hans Verkuil wrote: > 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. What do you mean, drop what altogether ? > > + </row> > > </tbody> > > </tgroup> > > </table> -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
