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

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Message-ID: <058027df-1b1b-4c46-b8e1-ec53fc809e82@collabora.com>
Date: Sat, 29 Nov 2025 11:50:16 +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

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.

>> take the background color into account.  Therefore I had to capture the frame
>> CRCs at DisplayPort AUX channel level, by using the USB-C DP AltMode capable
> 
> Oh that sounds interesting! I'm not sure how complex it would be to
> implement.

That's already implemented, I plan to submit the patches soon.

> 
>> port of my RK3588-based board.  However, that solution is not yet available
>> upstream, as it requires further work for cleanup and improving the overall
>> USB-C reliability. 
>>
>> Hence I'll move on with your suggestion and switch to the simple bit-shifting
>> approach for the next revision.
>