linux-kernel - Re: [PATCH] drm/msm/dpu: disable gamma correction unit on SC7180

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Message-ID: <CAO9ioeUfZQVy7VFUp8FEVHN2_uL0ZB9jbkuexWY4D12YN_O3Jw@mail.gmail.com>
Date: Mon, 17 Nov 2025 13:51:29 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: Rob Clark <robin.clark@....qualcomm.com>,
        Dmitry Baryshkov <lumag@...nel.org>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Jessica Zhang <jesszhan0024@...il.com>, Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Federico Amedeo Izzo <federico@...o.pro>
Subject: Re: [PATCH] drm/msm/dpu: disable gamma correction unit on SC7180

On Mon, 17 Nov 2025 at 13:25, Konrad Dybcio
<konrad.dybcio@....qualcomm.com> wrote:
>
> On 11/15/25 4:08 AM, Dmitry Baryshkov wrote:
> > IGT reported test failures with Gamma correction block on SC7180.
> > Disable GC subblock on SC7180 until we trage the issue.
> >
> > Cc: Federico Amedeo Izzo <federico@...o.pro>
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
> > ---
> > Most likely I will squash this into the GC patch
> > ---
>
> Peeking at downstream, 7180 and 845 should have the exact same GC
> (v1.8).. it seems like there's an attempt to program it through
> REGDMA instead of regular reg access. Not sure if it's actually
> necessary or just an optimization

I think it's mostly an optimization.

> What tests are exactly failing? I couldn't track it down on FDO GL

See [1] and other failed SC7180 jobs from the same pipeline. I haven't
triaged it yet, but I assume this might be related to platform
resources (it has only 2 LM blocks and only 1 DSPP).
Another possibility is that maybe we need higher CFG bus bandwidth
when writing LUT registers.

[1] https://gitlab.freedesktop.org/drm/msm/-/jobs/87878393


-- 
With best wishes
Dmitry