Re: [PATCH v4 02/11] drm/fourcc: Add DRM_FORMAT_XV15/XV20

[Tomi Valkeinen]

Hi,

On 28/03/2025 00:34, Laurent Pinchart wrote:
> Hi Tomi,
>
> Thank you for the patch.
>
> On Wed, Mar 26, 2025 at 03:22:45PM +0200, Tomi Valkeinen wrote:
> > Add two new pixel formats:
> >
> > DRM_FORMAT_XV15 ("XV15")
> > DRM_FORMAT_XV20 ("XV20")
> >
> > The formats are 2 plane 10 bit per component YCbCr, with the XV15 2x2
> > subsampled whereas XV20 is 2x1 subsampled.
> >
> > Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
> > Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/drm_fourcc.c  | 6 ++++++
> >   include/uapi/drm/drm_fourcc.h | 8 ++++++++
> >   2 files changed, 14 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c
> > index 2f5781f5dcda..e101d1b99aeb 100644
> > --- a/drivers/gpu/drm/drm_fourcc.c
> > +++ b/drivers/gpu/drm/drm_fourcc.c
> > @@ -346,6 +346,12 @@ const struct drm_format_info *__drm_format_info(u32 format)
> >   		{ .format = DRM_FORMAT_P030,            .depth = 0,  .num_planes = 2,
> >   		  .char_per_block = { 4, 8, 0 }, .block_w = { 3, 3, 0 }, .block_h = { 1, 1, 0 },
> >   		  .hsub = 2, .vsub = 2, .is_yuv = true},
> > +		{ .format = DRM_FORMAT_XV15,		.depth = 0,  .num_planes = 2,
> > +		  .char_per_block = { 4, 8, 0 }, .block_w = { 3, 3, 0 }, .block_h = { 1, 1, 0 },
> > +		  .hsub = 2, .vsub = 2, .is_yuv = true },
> > +		{ .format = DRM_FORMAT_XV20,		.depth = 0,  .num_planes = 2,
> > +		  .char_per_block = { 4, 8, 0 }, .block_w = { 3, 3, 0 }, .block_h = { 1, 1, 0 },
> > +		  .hsub = 2, .vsub = 1, .is_yuv = true },
>
> It appears we can never have too much (or enough) documentation, as
> reading the format info documentation leaves me with unanswered
> questions.
>
> Looking at drm_format_info_min_pitch():
>
> uint64_t drm_format_info_min_pitch(const struct drm_format_info *info,
> 				   int plane, unsigned int buffer_width)
> {
> 	if (!info || plane < 0 || plane >= info->num_planes)
> 		return 0;
>
> 	return DIV_ROUND_UP_ULL((u64)buffer_width * info->char_per_block[plane],
> 			    drm_format_info_block_width(info, plane) *
> 			    drm_format_info_block_height(info, plane));
> }
>
> For the first plane, the function will return `buffer_width * 4 / 3`
> (rouding up), which I think is right. For the second plane, it will
> return `buffer_width * 8 / 3`, which I believe is wrong as the format is
> subsampled by a factor 2 horizontally. It seems that either
> char_per_block and block_w need to take horizontal subsampling into
> account (and therefore be 8 and 6 for the second plane), or
> drm_format_info_min_pitch() should consider .hsub. Or there's something
> else I'm missing :-)

The buffer_width is already divided by the hsub, in 
drm_format_info_plane_width().

> >   	};
> >   
> >   	unsigned int i;
> > diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
> > index 81202a50dc9e..1247b814bd66 100644
> > --- a/include/uapi/drm/drm_fourcc.h
> > +++ b/include/uapi/drm/drm_fourcc.h
> > @@ -304,6 +304,14 @@ extern "C" {
> >   #define DRM_FORMAT_RGB565_A8	fourcc_code('R', '5', 'A', '8')
> >   #define DRM_FORMAT_BGR565_A8	fourcc_code('B', '5', 'A', '8')
> >   
> > +/*
> > + * 2 plane 10 bit per component YCrCb
> > + * index 0 = Y plane, [31:0] x:Y2:Y1:Y0 2:10:10:10 little endian
> > + * index 1 = Cb:Cr plane, [63:0] x:Cr2:Cb2:Cr1:x:Cb1:Cr0:Cb0 2:10:10:10:2:10:10:10 little endian
>
> I believe this is right, but I have a hard time validating it, as I
> think the corresponding figures in UG1085 are incorrect (they show a
> 8bpp format as far as I can tell). Do I assume correctly that you've
> tested the formats ?

Yes. kms++'s master branch has support for all the formats in this series.

 Tomi