Re: P010 fourcc format support - Was: Re: Kernel error "Unknown pixelformat 0x00000000" occurs when I start capture video

[Nicolas Dufresne <nicolas@ndufresne.ca>]

Le mercredi 09 janvier 2019 à 15:28 -0200, Mauro Carvalho Chehab a
écrit :
> Em Wed, 09 Jan 2019 11:52:45 -0500
> Nicolas Dufresne <nicolas@ndufresne.ca> escreveu:
> 
> > Le jeudi 10 janvier 2019 à 00:42 +0800, Ayaka a écrit :
> > > > There is a UVC media device that supports P010 device. We're discussing
> > > > about adding support for it on media. The full thread is at:
> > > > 
> > > > https://lore.kernel.org/linux-media/20190109121900.hbrpttmxz3gaotwx@valkosipuli.retiisi.org.uk/T/#m8c395156ca0e898e4c8b1e2c6309d912bc414804
> > > > 
> > > > We've seen that you tried to submit a patch series for DRM adding
> > > > support for it at the rockship driver. What's the status of such
> > > > series?  
> > > Rockchip would use another 10bit variant of NV12, which is merged as NV12LE40 at Gstreamer and I sent another patch for it, but I didn’t receive any feedback from that.  
> 
> Hmm... We have already NV12 format at media subsystem side:
> Documentation/media/uapi/v4l/pixfmt-nv12.rst
> 
> Did we miss some patch from you?

NV12 is by definition 8bit per pixel. Rockchip uses a 10bit variant,
for which each pixels is packed over 40 bits so that it's bandwidth
efficient. It's probably quite complex to handle HW wise. Xilinx also
got a variant they are upstream, which is packed over 32 bits, with 2
bits padding.

> 
> > For extra detail, the Rockchip variant is fully packed, with no padding
> > bits, while the Microsoft variant uses 16bits per pixels, with 6bits
> > padding. It was a mistake to use P010 initially for the Rockchip
> > format.
> 
> Yeah, P010 format seems to be a waste of bandwidth. Yet, as we're
> now having devices using it (via uvcdriver), it would make sense to
> merge the single plane format for it. I would merge the P016 too, as
> P010 seems to be just a degradation of it.

It's meant for fast CPU indexing, which makes it odd as a streaming
format.

> 
> Ayaka,
> 
> Would it be possible for you to re-send the P010/P016 documentation
> for single plane, fixing the typo (simliar -> similar)?
> 
> Let's not merge the dual plane formats, as we don't need them
> yet at the Kernel.
> 
> Thanks,
> Mauro