linux-kernel - Re: [PATCH v2 04/10] drm/fourcc: Add DRM_FORMAT_Y10

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Message-ID: <CAMuHMdVnDBt9QbR2bPdKHWgQ7i-OYYJ14ndc270z-hejY=bUdA@mail.gmail.com>
Date: Wed, 15 Jan 2025 13:33:15 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc: Vishal Sagar <vishal.sagar@....com>, Anatoliy Klymenko <anatoliy.klymenko@....com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Laurent Pinchart <laurent.pinchart@...asonboard.com>, Michal Simek <michal.simek@....com>, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 04/10] drm/fourcc: Add DRM_FORMAT_Y10_LE32

Hi Tomi,

On Wed, Jan 15, 2025 at 12:11 PM Tomi Valkeinen
<tomi.valkeinen@...asonboard.com> wrote:
> On 15/01/2025 12:33, Geert Uytterhoeven wrote:
> > On Wed, Jan 15, 2025 at 10:04 AM Tomi Valkeinen
> > <tomi.valkeinen@...asonboard.com> wrote:
> >> Add Y10_LE32, a 10 bit greyscale format, with 3 pixels packed into
> >> 32-bit container.
> >>
> >> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
> >
> > 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.

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...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

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