Hi Tomi,
On Wed, Jan 15, 2025 at 1:42 PM Tomi Valkeinen
<tomi.valkeinen@xxxxxxxxxxxxxxxx> wrote:
> On 15/01/2025 14:33, Geert Uytterhoeven wrote:
> > On Wed, Jan 15, 2025 at 12:11 PM Tomi Valkeinen
> > <tomi.valkeinen@xxxxxxxxxxxxxxxx> wrote:
> >> On 15/01/2025 12:33, Geert Uytterhoeven wrote:
> >>> On Wed, Jan 15, 2025 at 10:04 AM Tomi Valkeinen
> >>> <tomi.valkeinen@xxxxxxxxxxxxxxxx> wrote:
> >>>> Add Y10_LE32, a 10 bit greyscale format, with 3 pixels packed into
> >>>> 32-bit container.
> >>>>
> >>>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
> >>>
> >>> Thanks for your patch!
> >>>
> >>>> --- a/include/uapi/drm/drm_fourcc.h
> >>>> +++ b/include/uapi/drm/drm_fourcc.h
> >>>> @@ -408,6 +408,7 @@ extern "C" {
> >>>> /* Greyscale formats */
> >>>>
> >>>> #define DRM_FORMAT_Y8 fourcc_code('G', 'R', 'E', 'Y') /* 8-bit Y-only */
> >>>> +#define DRM_FORMAT_Y10_LE32 fourcc_code('Y', 'P', 'A', '4') /* [31:0] x:Y2:Y1:Y0 2:10:10:10 little endian */
> >>>
> >>> R10_LE32? Or R10_PA4?
> >>
> >> Can we discuss the "R" vs "Y" question under the cover letter? There's
> >> some more context about it in there.
> >
> > Sorry, hadn't read the cover letter. I got attracted by "Y8" and "Y10".
> >
> >> I took the "LE32" from Gstreamer's format. Maybe it's a bit pointless.
> >>
> >> I don't know if it makes sense to add the fourcc to the DRM format name.
> >> The fourcc is very limited. Rather, we could, say, have
> >> DRM_FORMAT_Y10_PACKED_32 (or "R", if you insist =).
> >>
> >>> Does LE32 have a meaning? My first guess just reading the subject
> >>> was wrong ("little endian 32-bit" ;-)
> >>
> >> I'm not sure I follow. It's little-endian. The pixel group/unit is a
> >> 32-bit number, where the leftmost pixel on the screen is in bits 9-0,
> >> and the padding is in bits 31-30, and stored in memory as little-endian.
> >
> > Ah, the "LE" applies to the pixels inside each word.
>
> No, to the 32-bit container.
>
> > DRM formats stored in memory are always little-endian, unless the
> > DRM_FORMAT_BIG_ENDIAN bit is set, which is what I was hinting
> > at...
>
> Indeed you're right. The "LE" is pointless. So back to the bike-shedding
> about the name =).
As the order inside the container is Y2:Y1:Y0, it _is_ little endian.
Cfr.
#define DRM_FORMAT_YUYV fourcc_code('Y', 'U', 'Y', 'V') /* [31:0]
Cr0:Y1:Cb0:Y0 8:8:8:8 little endian */
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
