[libcamera-devel] [PATCH 2/3] libcamera: v4l2_videodevice: Clarify setting of v4l2_buffer timestamp

[Kieran Bingham]

Quoting Laurent Pinchart via libcamera-devel (2022-03-23 00:13:59)
> Hi Umang,
> 
> Thank you for the patch.
> 
> On Thu, Mar 17, 2022 at 04:17:39PM +0530, Umang Jain via libcamera-devel wrote:
> > Add a comment to clarify why we set v4l2_buffer timestamp while
> > queuing the buffer (VIDIOC_QBUF). The timstamps are required to
> > be supplied for memory-to-memory devices for output streams which
> > then are copied to capture stream buffers with the help of
> > V4L2_BUF_FLAG_TIMESTAMP_COPY (set by the driver).
> > 
> > Signed-off-by: Umang Jain <umang.jain at ideasonboard.com>
> > ---
> >  src/libcamera/v4l2_videodevice.cpp | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
> > index 5580269f..a6c54b19 100644
> > --- a/src/libcamera/v4l2_videodevice.cpp
> > +++ b/src/libcamera/v4l2_videodevice.cpp
> > @@ -1600,6 +1600,14 @@ int V4L2VideoDevice::queueBuffer(FrameBuffer *buffer)
> >                       buf.length = planes[0].length;
> >               }
> >  
> > +             /*
> > +              * Timestamps are to be supplied if the device is a mem-to-mem
> > +              * device. The drivers will have V4L2_BUF_FLAG_TIMESTAMP_COPY
> > +              * set hence these timestamps will be copied from the output
> > +              * buffers to capture buffers. If the device is not mem-to-men,
> 
> s/mem-to-men/mem-to-mem/
> 
> > +              * there is no harm in setting the timestamps as they will be
> > +              * ignored (and over-written).
> 
> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

> 
> > +              */
> >               buf.timestamp.tv_sec = metadata.timestamp / 1000000000;
> >               buf.timestamp.tv_usec = (metadata.timestamp / 1000) % 1000000;
> >       }
> 
> -- 
> Regards,
> 
> Laurent Pinchart