linux-kernel - Re: [PATCH v7 03/11] drm/fourcc: Add DRM_FORMAT

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Message-ID: <116b508e-0853-4b0b-966e-47d84167d4be@ideasonboard.com>
Date: Wed, 28 Jan 2026 17:38:11 +0200
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Laurent Pinchart <laurent.pinchart@...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>,
 Michal Simek <michal.simek@....com>, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 Geert Uytterhoeven <geert@...ux-m68k.org>,
 Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
 Pekka Paalanen <ppaalanen@...il.com>,
 Pekka Paalanen <pekka.paalanen@...labora.com>,
 Dmitry Baryshkov <lumag@...nel.org>
Subject: Re: [PATCH v7 03/11] drm/fourcc: Add DRM_FORMAT_Y8

Hi,

On 28/01/2026 13:49, Laurent Pinchart wrote:
> Hi Tomi,
> 
> Thank you for the patch.
> 
> On Mon, Dec 01, 2025 at 02:18:45PM +0200, Tomi Valkeinen wrote:
>> Add greyscale Y8 format.
> 
> I would explain here why we need a new format and can't just use
> DRM_FORMAT_R8. You don't need to convince me, but I think it's important
> to summarize the rationale should someone later wonder why we introduced
> this.
> 
>> Acked-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
>> Reviewed-by: Pekka Paalanen <pekka.paalanen@...labora.com>
>> Reviewed-by: Vishal Sagar <vishal.sagar@....com>
>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
>> ---
>>  drivers/gpu/drm/drm_fourcc.c  |  1 +
>>  include/uapi/drm/drm_fourcc.h | 10 ++++++++++
>>  2 files changed, 11 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c
>> index b22ef86428a1..a39b9d7a5b62 100644
>> --- a/drivers/gpu/drm/drm_fourcc.c
>> +++ b/drivers/gpu/drm/drm_fourcc.c
>> @@ -275,6 +275,7 @@ const struct drm_format_info *__drm_format_info(u32 format)
>>  		{ .format = DRM_FORMAT_YVU422,		.depth = 0,  .num_planes = 3, .cpp = { 1, 1, 1 }, .hsub = 2, .vsub = 1, .is_yuv = true },
>>  		{ .format = DRM_FORMAT_YUV444,		.depth = 0,  .num_planes = 3, .cpp = { 1, 1, 1 }, .hsub = 1, .vsub = 1, .is_yuv = true },
>>  		{ .format = DRM_FORMAT_YVU444,		.depth = 0,  .num_planes = 3, .cpp = { 1, 1, 1 }, .hsub = 1, .vsub = 1, .is_yuv = true },
>> +		{ .format = DRM_FORMAT_Y8,		.depth = 8,  .num_planes = 1, .cpp = { 1, 0, 0 }, .hsub = 1, .vsub = 1, .is_yuv = true },
>>  		{ .format = DRM_FORMAT_NV12,		.depth = 0,  .num_planes = 2, .cpp = { 1, 2, 0 }, .hsub = 2, .vsub = 2, .is_yuv = true },
>>  		{ .format = DRM_FORMAT_NV21,		.depth = 0,  .num_planes = 2, .cpp = { 1, 2, 0 }, .hsub = 2, .vsub = 2, .is_yuv = true },
>>  		{ .format = DRM_FORMAT_NV16,		.depth = 0,  .num_planes = 2, .cpp = { 1, 2, 0 }, .hsub = 2, .vsub = 1, .is_yuv = true },
>> diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
>> index 6c786701238e..5cfc188c4e72 100644
>> --- a/include/uapi/drm/drm_fourcc.h
>> +++ b/include/uapi/drm/drm_fourcc.h
>> @@ -459,6 +459,16 @@ extern "C" {
>>  #define DRM_FORMAT_YUV444	fourcc_code('Y', 'U', '2', '4') /* non-subsampled Cb (1) and Cr (2) planes */
>>  #define DRM_FORMAT_YVU444	fourcc_code('Y', 'V', '2', '4') /* non-subsampled Cr (1) and Cb (2) planes */
>>  
>> +/*
>> + * 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.
>> + *
> 
> Extra blank line.

I'll drop.

>> + */
>> +
>> +#define DRM_FORMAT_Y8		fourcc_code('G', 'R', 'E', 'Y')  /* 8-bit Y-only */
> 
> I would have gone for 'Y', '8', ' ', ' '
Missed these comments earlier...

Yes, "Y8  " makes sense. But I was trying to be nice, as there are
already users for Y8 ("GREY") with BSP kernels, and changing the fourcc
code would break their userspace...

 Tomi