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 15:54:19 +0100
From: Werner Sembach <wse@...edocomputers.com>
To: Andri Yngvason <andri@...vason.is>
Cc: Maxime Ripard <mripard@...nel.org>,
 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 14:42 schrieb Andri Yngvason:
> mið., 10. jan. 2024 kl. 13:09 skrifaði Werner Sembach<wse@...edocomputers.com>:
>> 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/
> Well, I've implemented this for sway and wlroots now and Simon has
> reacted positively, so this does appear likely to end up as a feature
> in wlroots based compositors.
>
>> 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.
>>
> You can send the patches to me if you want and I can see if they're
> useful. I'm really only interested in the color format part though.
> Alternatively, you can continue your work and post it to LKML and I
> can focus on the userspace side and testing. By the way, I have an
> HDMI analyzer that can tell me the actual color format.

Searched for what I still had in my private repo, see attachments, filename is 
the branch name I used and like I said: I don't know which state these branches 
are in.

The hacking_ branch was based on 25fe90f43fa312213b653dc1f12fd2d80f855883 from 
linux-next and the rejected_ one on 132b189b72a94328f17fd70321bfe63e5b4208e9 
from drm-tip.

And the rejected_ one is 2 weeks newer.

To pick it up again I would first need to allocate some time for it, ... which 
could take some time.

With a HDMI analyzer at hand you are better equipped then me already. I was 
working with printf statements, Monitor OSD's and test patterns like 
https://media.extron.com/public/technology/landing/vector4k/img/scalfe-444Chroma.png 
and http://www.lagom.nl/lcd-test/ while being red blind xD.

>
> Thanks,
> Andri
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