linux-kernel - Re: [PATCH 5/7] drm/uAPI: Add "preferred color format" drm property as setting for userspace

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Date: Wed, 10 Jan 2024 14:09:11 +0100
From: Werner Sembach <wse@...edocomputers.com>
To: Andri Yngvason <andri@...vason.is>, Maxime Ripard <mripard@...nel.org>
Cc: Harry Wentland <harry.wentland@....com>, Leo Li <sunpeng.li@....com>,
 Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
 Alex Deucher <alexander.deucher@....com>,
 Christian König <christian.koenig@....com>,
 "Pan, Xinhui" <Xinhui.Pan@....com>, David Airlie <airlied@...il.com>,
 Daniel Vetter <daniel@...ll.ch>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Thomas Zimmermann <tzimmermann@...e.de>,
 Jani Nikula <jani.nikula@...ux.intel.com>,
 Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
 Rodrigo Vivi <rodrigo.vivi@...el.com>,
 Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
 amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
 Simon Ser <contact@...rsion.fr>, Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [PATCH 5/7] drm/uAPI: Add "preferred color format" drm property
 as setting for userspace

Hi,

Am 10.01.24 um 11:11 schrieb Andri Yngvason:
> Hi,
>
> mið., 10. jan. 2024 kl. 09:27 skrifaði Maxime Ripard <mripard@...nel.org>:
>> On Tue, Jan 09, 2024 at 06:11:02PM +0000, Andri Yngvason wrote:
>>> From: Werner Sembach <wse@...edocomputers.com>
>>>
>>> Add a new general drm property "preferred color format" which can be used
>>> by userspace to tell the graphic drivers to which color format to use.
>>>
>>> Possible options are:
>>>      - auto (default/current behaviour)
>>>      - rgb
>>>      - ycbcr444
>>>      - ycbcr422 (not supported by both amdgpu and i915)
>>>      - ycbcr420
>>>
>>> In theory the auto option should choose the best available option for the
>>> current setup, but because of bad internal conversion some monitors look
>>> better with rgb and some with ycbcr444.
>> I looked at the patch and I couldn't find what is supposed to happen if
>> you set it to something else than auto, and the driver can't match that.
>> Are we supposed to fallback to the "auto" behaviour, or are we suppose
>> to reject the mode entirely?
>>
>> The combination with the active output format property suggests the
>> former, but we should document it explicitly.
> It is also my understanding that it should fall back to the "auto"
> behaviour. I will add this to the documentation.

Yes, that was the intention, and then userspace can check, but it wasn't well 
received: https://gitlab.freedesktop.org/drm/amd/-/issues/476#note_964530

Actually a lot of the thoughts that went into the original patch set can be 
found in that topic.

There was another iteration of the patch set that I never finished and sent to 
the LKML because I got discouraged by this: 
https://lore.kernel.org/dri-devel/20210623102923.70877c1a@eldfell/

I can try to dig it up, but it is completely untested and I don't think I still 
have the respective TODO list anymore, so I don't know if it is a better or 
worst starting point than the last iteration I sent to the LKML.

Greetings

Werner

>
> Thanks,
> Andri