Re: [PATCH v8 04/11] drm/fourcc: Add DRM_FORMAT_Y10_P32

[Simon Ser]

On Friday, March 20th, 2026 at 11:48, Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx> wrote:

> Hi,
> 
> On 19/03/2026 16:59, Simon Ser wrote:
> > On Wednesday, January 28th, 2026 at 18:25, Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx> wrote:
> >
> >> Add Y10_P32, a 10 bit greyscale format, with 3 pixels packed into
> >> 32-bit container.
> >>
> >> The fourcc for the format is 'YPA4', which comes from Y - Y only, P -
> >> packed, A - 10 (as in 0xA), 4 - 4 bytes.
> >
> > I know we aren't super consistent about DRM format names, but… this _P32
> > suffix doesn't make sense to me: we never had it before, and a lot of
> > DRM formats are packed (in the Vulkan sense [1]), so I'm not sure why
> > this one would need it.
> >
> > What's special about this one is that it's the first (AFAIK) which has
> > 3 pixels per block. Some YCbCr formats are sub-sampled, but always use a
> > square block.
> >
> > I would suggest something like YYYX1010102. We use the "channels
> > followed by bits per component" pattern elsewhere.
> I'm ok with that. But wouldn't it be XYYY2101010 instead?

Oh yes, indeed.

> And then we just wait for someone to add a x:Y0:Y1:Y2 format (instead of
> x:Y2:Y1:Y0). Should we be more specific, and already make this one
> XY2Y1Y0_2101010...

Looking at all existing YCbCr formats, they all use the Y2-Y1-Y0 ordering,
none of them use the reverse. So I'd say it's safe enough to just leave it
out and treat it as the default. We can think of a new pattern if/when we
hit the reverse case.