Re: [PATCH v6 2/8] media: v4l: Add definition for Allwinner's MB32-tiled NV12 format

[Paul Kocialkowski <paul.kocialkowski-LDxbnhwyfcJBDgjK7y7TUQ@public.gmane.org>]

[-- Attachment #1: Type: text/plain, Size: 4981 bytes --]

Hi,

On Sat, 2018-08-04 at 13:42 +0200, Hans Verkuil wrote:
> On 07/25/2018 12:02 PM, Paul Kocialkowski wrote:
> > This introduces support for Allwinner's MB32-tiled NV12 format, where
> > each plane is divided into macroblocks of 32x32 pixels. Hence, the size
> > of each plane has to be aligned to 32 bytes. The pixels inside each
> > macroblock are coded as they would be if the macroblock was a single
> > plane, line after line.
> > 
> > The MB32-tiled NV12 format is used by the video engine on Allwinner
> > platforms: it is the default format for decoded frames (and the only one
> > available in the oldest supported platforms).
> > 
> > Signed-off-by: Paul Kocialkowski <paul.kocialkowski-LDxbnhwyfcJBDgjK7y7TUQ@public.gmane.org>
> > ---
> >  Documentation/media/uapi/v4l/pixfmt-reserved.rst | 15 ++++++++++++++-
> >  drivers/media/v4l2-core/v4l2-ioctl.c             |  1 +
> >  include/uapi/linux/videodev2.h                   |  1 +
> >  3 files changed, 16 insertions(+), 1 deletion(-)
> > 
> > diff --git a/Documentation/media/uapi/v4l/pixfmt-reserved.rst b/Documentation/media/uapi/v4l/pixfmt-reserved.rst
> > index 38af1472a4b4..9a68b6a787bf 100644
> > --- a/Documentation/media/uapi/v4l/pixfmt-reserved.rst
> > +++ b/Documentation/media/uapi/v4l/pixfmt-reserved.rst
> > @@ -243,7 +243,20 @@ please make a proposal on the linux-media mailing list.
> >  	It is an opaque intermediate format and the MDP hardware must be
> >  	used to convert ``V4L2_PIX_FMT_MT21C`` to ``V4L2_PIX_FMT_NV12M``,
> >  	``V4L2_PIX_FMT_YUV420M`` or ``V4L2_PIX_FMT_YVU420``.
> > -
> > +    * .. _V4L2-PIX-FMT-MB32-NV12:
> > +
> > +      - ``V4L2_PIX_FMT_MB32_NV12``
> > +      - 'MN12'
> > +      - Two-planar NV12-based format used by the Allwinner video engine
> > +        hardware, with 32x32 tiles for the luminance plane and 32x64 tiles
> > +        for the chrominance plane. Each tile is a linear pixel data
> > +        representation within its own bounds. Each tile follows the previous
> > +        one linearly (as in, from left to right, top to bottom).
> 
> as in, -> as in:

Thanks!

> > +
> > +        The frame dimensions are aligned to match an integer number of
> > +        tiles, resulting in 32-aligned resolutions for the luminance plane
> > +        and 16-aligned resolutions for the chrominance plane (with 2x2
> > +        subsampling).
> >  
> >  .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
> >  
> > diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> > index 68e914b83a03..7e1c200de10d 100644
> > --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> > +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> > @@ -1331,6 +1331,7 @@ static void v4l_fill_fmtdesc(struct v4l2_fmtdesc *fmt)
> >  		case V4L2_PIX_FMT_SE401:	descr = "GSPCA SE401"; break;
> >  		case V4L2_PIX_FMT_S5C_UYVY_JPG:	descr = "S5C73MX interleaved UYVY/JPEG"; break;
> >  		case V4L2_PIX_FMT_MT21C:	descr = "Mediatek Compressed Format"; break;
> > +		case V4L2_PIX_FMT_MB32_NV12:	descr = "Allwinner tiled NV12 format"; break;
> 
> "Allwinner Tiled NV12 Format"
> 
> If it is Allwinner specific, then that should be in the PIX_FMT name as well:
> something like V4L2_PIX_FMT_ALLWINNER_MB32_NV12 or perhaps SUNXI_MB32_NV12.
> 
> On the other hand, you could also see this as a variant of e.g. V4L2_PIX_FMT_NV12MT
> or V4L2_PIX_FMT_NV12MT_16X16. In that case it is not necessarily Allwinner specific
> since other devices might choose this format. You can go either way, as long
> as it is consistent.

I think it is fair to say that the format is Allwinner-specific and
unlikely to be found elsewhere. It is not actually very well described
by "MB32" since the chroma tiles have a different pixel size than the
luma tiles (16x64).

It would probably be clearer to just call the format:
V4L2_PIX_FMT_SUNXI_TILED_NV12

Cheers,

Paul

> >  		default:
> >  			WARN(1, "Unknown pixelformat 0x%08x\n", fmt->pixelformat);
> >  			if (fmt->description[0])
> > diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> > index d171361ed9b3..453d27142e31 100644
> > --- a/include/uapi/linux/videodev2.h
> > +++ b/include/uapi/linux/videodev2.h
> > @@ -670,6 +670,7 @@ struct v4l2_pix_format {
> >  #define V4L2_PIX_FMT_Z16      v4l2_fourcc('Z', '1', '6', ' ') /* Depth data 16-bit */
> >  #define V4L2_PIX_FMT_MT21C    v4l2_fourcc('M', 'T', '2', '1') /* Mediatek compressed block mode  */
> >  #define V4L2_PIX_FMT_INZI     v4l2_fourcc('I', 'N', 'Z', 'I') /* Intel Planar Greyscale 10-bit and Depth 16-bit */
> > +#define V4L2_PIX_FMT_MB32_NV12 v4l2_fourcc('M', 'N', '1', '2') /* Allwinner tiled NV12 format */
> >  
> >  /* 10bit raw bayer packed, 32 bytes for every 25 pixels, last LSB 6 bits unused */
> >  #define V4L2_PIX_FMT_IPU3_SBGGR10	v4l2_fourcc('i', 'p', '3', 'b') /* IPU3 packed 10-bit BGGR bayer */
> > 
> 
> Regards,
> 
> 	Hans
-- 
Paul Kocialkowski, Bootlin (formerly Free Electrons)
Embedded Linux and kernel engineering
https://bootlin.com