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

[paul.elder at ideasonboard.com]

On Fri, Jul 08, 2022 at 12:20:14AM +0300, Laurent Pinchart wrote:
> 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.

Yeah I guess we could wait then.

I'll change the next patch to just YUV422 then.


Paul

> 
> > 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;
> >  }
> >  
> >  /**