[libcamera-devel] [PATCH 2/4] libcamera: v4l2_pixelformat: Use multiplanar if single is unavailable

[Laurent Pinchart]

Hi Paul,

Thank you for the patch.

On Fri, Jul 08, 2022 at 12:03:08AM +0900, Paul Elder via libcamera-devel wrote:
> Some formats, such as YVU422 (but *not* YUV422), YUV444, and YVU444,
> have only a multiplanar v4l2 format and no singleplanar format. When
> using V4L2PixelFormat::fromPixelFormat() to convert a libcamera format
> to V4L2PixelFormat, the default is to fetch the singleplanar format, and
> for those three formats an invalid format will be returned. The caller
> shouldn't be expected to check first if it should request the
> singleplanar or multiplanar version (that's the whole point of
> V4L2PixelFormat::fromPixelFormat()), so the solution that this patch
> implements is if fetching singleplanar/multiplanar fails, try fetching
> the other one.
> 
> The side effect is that as most formats have only singleplanar v4l2
> format and no multiplanar format, if a multiplanar format is request for
> these formats then the singleplanar one will be automatically returned.
> Since currently all callers of V4L2PixelFormat::fromPixelFormat() use
> the default singleplanar call, it is reasoned that this is not an issue.

Jacopo is planning to rework this to add JPEG support in addition to
MJPEG, with a mechanism that should address your problem in a better way
(taking into account the formats actually supported by the device). We
could merge this as a quick workaround, but if there's no urgency, I'd
wait for Jacopo's patch.

> Signed-off-by: Paul Elder <paul.elder at ideasonboard.com>
> ---
>  src/libcamera/v4l2_pixelformat.cpp | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/src/libcamera/v4l2_pixelformat.cpp b/src/libcamera/v4l2_pixelformat.cpp
> index 58fc4e9d..0d2bc350 100644
> --- a/src/libcamera/v4l2_pixelformat.cpp
> +++ b/src/libcamera/v4l2_pixelformat.cpp
> @@ -321,7 +321,14 @@ V4L2PixelFormat V4L2PixelFormat::fromPixelFormat(const PixelFormat &pixelFormat,
>  	if (!info.isValid())
>  		return V4L2PixelFormat();
>  
> -	return multiplanar ? info.v4l2Formats.multi : info.v4l2Formats.single;
> +	V4L2PixelFormat ret = multiplanar ? info.v4l2Formats.multi
> +					  : info.v4l2Formats.single;
> +	/* Try the other of multi/single if the proper one doesn't exist */
> +	if (!ret.isValid())
> +		ret = multiplanar ? info.v4l2Formats.single
> +				  : info.v4l2Formats.multi;
> +
> +	return ret;
>  }
>  
>  /**

-- 
Regards,

Laurent Pinchart