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

[Kieran Bingham]

Hi Hans,

So the IPU6 enablement in the simple pipeline handler is straight
forward ... lets see what we can do here.

Quoting Hans de Goede (2024-07-03 16:09:22)
> The /dev/video# nodes of the IPU6 driver set both V4L2_CAP_VIDEO_CAPTURE
> and V4L2_CAP_META_CAPTURE.

Is this a driver that is already upstream?

Is it really valid to set both of those in the V4L2 spec?

If so - then we have to do something here... if not - what control do we
have to fix the current driver?

> 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.
> 
> 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 9057be08..fdd877c8 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 */

If this is a workaround, and really not expected I would want more
detail here. Especially if this is a short term workaround for any
possibly out of tree or staging drivers (I haven't checked where IPU6
state is currently), including a \todo: to remove it in the future
when the driver is fixed/upstreamed.

Howevfer if it's simply entirely within the rights of a v4l2 driver to
set both - then I think the comment would stand and be valid on it's
own, but some how we'd have to stay aware or document somewhere else in
the doxygen for this class that we directly treat devices as video
devices if they report both video and metadata capture.

--
Kieran

> +               if (isVideo())
> +                       return false;
> +
>                 return device_caps() & (V4L2_CAP_META_CAPTURE |
>                                         V4L2_CAP_META_OUTPUT);
>         }
> -- 
> 2.45.1
>