linux-kernel - Re: [PATCH v4 03/11] drm/fourcc: Add DRM_FORMAT

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Message-ID: <20250425131817.01b7f7d9@eldfell>
Date: Fri, 25 Apr 2025 13:18:17 +0300
From: Pekka Paalanen <pekka.paalanen@...labora.com>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>, Geert Uytterhoeven
 <geert@...ux-m68k.org>, 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>, Michal Simek <michal.simek@....com>,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, Dmitry Baryshkov
 <dmitry.baryshkov@....qualcomm.com>
Subject: Re: [PATCH v4 03/11] drm/fourcc: Add DRM_FORMAT_Y8

On Fri, 25 Apr 2025 11:38:28 +0300
Tomi Valkeinen <tomi.valkeinen@...asonboard.com> wrote:

> Hi Pekka,
> 
> On 17/04/2025 11:13, Pekka Paalanen wrote:
> >> My understanding is that the Y-only pixel formats behave in a well
> >> defined way (or, as well defined as the YUV formats), and there's
> >> nothing more to add here. Is that right?  
> > 
> > There are two things:
> > 
> > - Y8 follows COLOR_RANGE property, just like all other YUV formats.
> > - Y8 implies that Cb and Cr are both neutral (0.0 in nominal values).
> > 
> > I'd like these explicitly written down, so that they become obvious to
> > everyone. I suspect either one might be easy to forget when writing
> > code and taking shortcuts without thinking.  
> 
> I didn't find a suitable place in the docs for this, but would this, in 
> the drm_fourcc.h, be enough:
> 
> /*
>   * Y-only (greyscale) formats
>   *
>   * The Y-only formats are handled similarly to the YCbCr formats in the 
> display
>   * pipeline, with the Cb and Cr implicitly neutral (0.0 in nominal 
> values). This
>   * also means that COLOR_RANGE property applies to the Y-only formats.
>   *
>   */
> 
> #define DRM_FORMAT_Y8		fourcc_code('G', 'R', 'E', 'Y')  /* 8-bit Y-only */
> #define DRM_FORMAT_Y10_P32	fourcc_code('Y', 'P', 'A', '4')  /* [31:0] 
> x:Y2:Y1:Y0 2:10:10:10 little endian */
> 

Hi Tomi,

I would be very happy with that.


Thanks,
pq

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