[PATCH 1/2] libcamera: v4l2_videodevice: Fix devices which set both V4L2_CAP_VIDEO and V4L2_CAP_META

[Naushir Patuck]

Hi all,

On Wed, 1 May 2024 at 12:58, Hans de Goede <hdegoede at redhat.com> wrote:
>
> Hi Laurent,
>
> On 5/1/24 12:11 AM, Laurent Pinchart wrote:
> > Hi Hans,
> >
> > Thank you for the patch.
> >
> > On Tue, Apr 30, 2024 at 07:17:27PM +0200, Hans de Goede wrote:
> >> The /dev/video# nodes of the IPU6 driver set both V4L2_CAP_VIDEO_CAPTURE
> >> and V4L2_CAP_META_CAPTURE.
> >>
> >> This was resulting in V4L2VideoDevice::getFormat() / tryFormat() /
> >> setFormat() calling the metadata related ioctls instead of the videocap
> >> ioctls causing things to not work.
> >>
> >> Fix this by making V4L2Capability::isMeta() return false when the device
> >> also has one of the video capabilities.
> >
> > This seems to be a quick hack. What would it take to solve the issue
> > correctly ?
>
> I honestly don't know. Since the whole metadata stuff is all new
> and somewhat in flux I think properly fixing this is best
> delayed until we actually figure out what we want to do here /
> how this all is going to work.

The Pi 5 CFE driver also ran into this issue as we had a dev node that
advertised both meta and video caps.  I briefly looked into a fix, but
quickly came to the conclusion that it might need a larger rework job
than I was able to do at the time.  Instead we fixed the dev node to
only advertise either meta or video cap type, not both.

IIRC, a change would be needed to look at the pixel format set into
the V4L2VideoDevice object, decide if it is a meta or video format,
and then make the appropriate IOCTL calls after that.

Regards,
Naush

>
> Regards,
>
> Hans
>
>
>
> >
> >> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
> >> ---
> >>  include/libcamera/internal/v4l2_videodevice.h | 4 ++++
> >>  1 file changed, 4 insertions(+)
> >>
> >> diff --git a/include/libcamera/internal/v4l2_videodevice.h b/include/libcamera/internal/v4l2_videodevice.h
> >> index d157a447..5816c18d 100644
> >> --- a/include/libcamera/internal/v4l2_videodevice.h
> >> +++ b/include/libcamera/internal/v4l2_videodevice.h
> >> @@ -92,6 +92,10 @@ struct V4L2Capability final : v4l2_capability {
> >>      }
> >>      bool isMeta() const
> >>      {
> >> +            /* Treat devs which combine video and meta as video not meta */
> >
> > s/devs/devices/
> > s/meta/metadata/g
> >
> >> +            if (isVideo())
> >> +                    return false;
> >> +
> >>              return device_caps() & (V4L2_CAP_META_CAPTURE |
> >>                                      V4L2_CAP_META_OUTPUT);
> >>      }
> >
>