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

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Message-ID: <8541a10d-99ca-43d2-bafa-8e33bba01382@oss.qualcomm.com>
Date: Mon, 17 Nov 2025 13:09:59 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....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 11/17/25 12:51 PM, Dmitry Baryshkov wrote:
> 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

igt.kms_color@...ma.log fails, we get an ENAVAIL (-119) (which doesn't
seem like a good return value for this error but anyway..), dmesg says

05:42:13.199: [   75.472174] [drm:_dpu_rm_check_lm_and_get_connected_blks] [dpu error]failed to get dspp on lm 0
05:42:13.199: [   75.481487] [drm:_dpu_rm_make_reservation] [dpu error]unable to find appropriate mixers
05:42:13.199: [   75.490235] [drm:dpu_rm_reserve] [dpu error]failed to reserve hw resources: -119

which comes from:

idx = lm_cfg->dspp - DSPP_0;
if (idx < 0 || idx >= ARRAY_SIZE(rm->dspp_blks)) {
	// misleading error message, it's not LM%d, but DSPP%d
	DPU_ERROR("failed to get dspp on lm %d\n", lm_cfg->dspp);
	return false;
}

which comes from:

static const struct dpu_lm_cfg sc7180_lm[] = {
        {
                .name = "lm_0", .id = LM_0,
                .base = 0x44000, .len = 0x320,
                .features = MIXER_MSM8998_MASK,
                .sblk = &sc7180_lm_sblk,
                .lm_pair = LM_1,
                .pingpong = PINGPONG_0,
                .dspp = DSPP_0,
        }, {
                .name = "lm_1", .id = LM_1,
                .base = 0x45000, .len = 0x320,
                .features = MIXER_MSM8998_MASK,
                .sblk = &sc7180_lm_sblk,
                .lm_pair = LM_0,
                .pingpong = PINGPONG_1,
		// no dspp here, errors out
        },
};

would simply binding .dspp = DSPP_0 to the other one just work here?

Also, would that mean we can only have gamma control on a single active
LM at a time?

Konrad