linux-kernel - Re: [PATCH] drm/vkms: Fix bad matrix offset component multiplication

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Message-ID: <58373d82-d238-4302-b72a-3625b153bd9e@collabora.com>
Date: Tue, 10 Feb 2026 14:24:15 -0300
From: Ariel D'Alessandro <ariel.dalessandro@...labora.com>
To: Louis Chauvet <louis.chauvet@...tlin.com>,
 Haneen Mohammed <hamohammed.sa@...il.com>, Simona Vetter <simona@...ll.ch>,
 Melissa Wen <melissa.srw@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 nfraprado@...labora.com, pekka.paalanen@...labora.com,
 daniels@...labora.com, kernel@...labora.com
Subject: Re: [PATCH] drm/vkms: Fix bad matrix offset component multiplication

Hi Louis,

Sorry for the delay.

On 12/29/25 6:33 AM, Louis Chauvet wrote:
> 
> 
> On 12/23/25 18:26, Ariel D'Alessandro wrote:
>> Pixels values are packed as 16-bit UNORM values, so the matrix offset
>> components must be multiplied properly by the idempotent element -i.e.
>> number 1 encoded as 16-bit UNORM-.
>>
>> Signed-off-by: Ariel D'Alessandro <ariel.dalessandro@...labora.com>
> 
> Hi,
> 
> Thanks for this patch!
> 
> How did you catch the issue? If you have an example of failing color 
> conversion, can you add a test case in vkms_color_test?
I found it while working on this IGT tools patch series [0], this patch 
in particular [1].

I've just added the related kunit test, so I'll send it as a v2 patchset.

[0] 
https://lore.kernel.org/igt-dev/20251223-post-blend-colorops-v2-0-f40aca9795bd@collabora.com/
[1] 
https://lore.kernel.org/igt-dev/20251223-post-blend-colorops-v2-7-f40aca9795bd@collabora.com/

Regards,

-- 
Ariel D'Alessandro
Software Engineer

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