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

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Message-ID: <d49d449b-7bbb-46fc-8e10-f04649d852f2@oss.qualcomm.com>
Date: Mon, 17 Nov 2025 14:39:32 +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 2:16 PM, Dmitry Baryshkov wrote:
> On Mon, 17 Nov 2025 at 14:10, Konrad Dybcio
> <konrad.dybcio@....qualcomm.com> wrote:
>>
>> 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?
> 
> Only LM_0 can use DSPP_0, that part is not flexible.

OK that makes sense

> 
>> Also, would that mean we can only have gamma control on a single active
>> LM at a time?
> 
> We can only control gamma on LM_0 on this platform.
> 
> BTW, the other log is more interesting:
> 
> [3] https://gitlab.freedesktop.org/drm/msm/-/jobs/87895515/viewer

I wonder if we need to take a closer look at this hunk:

/* Disable 8-bit rounding mode */
gc_lut->flags = 0;

also, IGT tests XRGB8888 - any chance the X is getting mistakenly
(un)modified?

Konrad