linux-kernel - Re: [PATCH v3 4/4] drm/rockchip: vop2: Support setting custom background color

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Message-ID: <012994e7-0e69-4885-8050-a404b7ae7608@collabora.com>
Date: Sat, 20 Dec 2025 00:42:05 +0200
From: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To: Chaoyi Chen <chaoyi.chen@...k-chips.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>,
 Sandy Huang <hjc@...k-chips.com>, Heiko Stübner
 <heiko@...ech.de>, Andy Yan <andy.yan@...k-chips.com>,
 Louis Chauvet <louis.chauvet@...tlin.com>,
 Haneen Mohammed <hamohammed.sa@...il.com>,
 Melissa Wen <melissa.srw@...il.com>
Cc: Robert Mader <robert.mader@...labora.com>, kernel@...labora.com,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH v3 4/4] drm/rockchip: vop2: Support setting custom
 background color

On 11/30/25 5:01 AM, Chaoyi Chen wrote:
> On 11/29/2025 5:50 PM, Cristian Ciocaltea wrote:
>> Hi Chaoyi,
>>
>> On 11/29/25 5:49 AM, Chaoyi Chen wrote:
>>> Hello Cristian, 
>>>
>>> On 11/28/2025 5:44 PM, Cristian Ciocaltea wrote:
>>>> The precision was something I initially looked into for CRC verification, in the
>>>> context of the related IGT test.  But since I've added the VKMS support, I think
>>>> we should not worry about that anymore. 
>>>>
>>>> Moreover, as already pointed out in [1], only RK3576 supports CRC generation at
>>>> display controller level, and that is not particularly useful because it doesn't
>>>
>>> I believe you can get the CRTC CRC on the RK3576, even when only the 
>>> background is visible and all plane is disabled. Feel free to let me
>>> know if you run into any issues :)
>>
>> Yes, CRTC CRC works on RK3576 for the planes, but not for the background, i.e.
>> the CRC is not updated when setting a different background color.  Unless
>> there's a way to change this default behavior, which I'm not aware of. 
>>
>> My current understanding is that the background color is applied at a later
>> stage in the display pipeline, *after* blending the planes and computing CRC.
>>
> 
> Which CRTC are you using? If you're using VP0, you might run into this
> problem. Please try VP1 instead.

Yeah, that's VP0 as there's only one HDMI output port on my Radxa ROCK 4D board.
I'll check if it's possible to switch to VP1.