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

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Message-ID: <b195971c-52e6-463e-a440-83dde4346e65@ideasonboard.com>
Date: Wed, 26 Mar 2025 15:55:18 +0200
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
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,
 Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
 Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Subject: Re: [PATCH v4 03/11] drm/fourcc: Add DRM_FORMAT_Y8

Hi,

On 26/03/2025 15:52, Geert Uytterhoeven wrote:
> Hi Tomi,
> 
> On Wed, 26 Mar 2025 at 14:23, Tomi Valkeinen
> <tomi.valkeinen@...asonboard.com> wrote:
>> Add greyscale Y8 format.
>>
>> Acked-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
>> 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
>> @@ -405,6 +405,9 @@ 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 */
>>
>> +/* Greyscale formats */
>> +
>> +#define DRM_FORMAT_Y8          fourcc_code('G', 'R', 'E', 'Y')  /* 8-bit Y-only */
> 
> This format differs from e.g. DRM_FORMAT_R8, which encodes
> the number of bits in the FOURCC format. What do you envision
> for e.g. DRM_FORMAT_Y16? fourcc_code('G', 'R', '1', '6')?

I wanted to use the same fourcc as on V4L2 side. Strictly speaking it's 
not required, but different fourccs for the same formats do confuse.

So, generally speaking, I'd pick an existing fourcc from v4l2 side if 
possible, and if not, invent a new one.

  Tomi