linux-kernel - Re: [PATCH RFT 13/14] drm/msm/a6xx: Drop cfg->ubwc

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Message-ID: <9010219f-a3f1-4869-84b3-b4f6c5e9f05f@oss.qualcomm.com>
Date: Fri, 9 May 2025 17:52:26 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Connor Abbott <cwabbott0@...il.com>
Cc: Konrad Dybcio <konradybcio@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <lumag@...nel.org>,
        Akhil P Oommen <quic_akhilpo@...cinc.com>, Sean Paul <sean@...rly.run>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org
Subject: Re: [PATCH RFT 13/14] drm/msm/a6xx: Drop cfg->ubwc_swizzle override

On 5/9/25 4:48 PM, Connor Abbott wrote:
> On Fri, May 9, 2025 at 9:37 AM Konrad Dybcio
> <konrad.dybcio@....qualcomm.com> wrote:
>>
>> On 5/9/25 3:17 PM, Konrad Dybcio wrote:
>>> On 5/8/25 9:26 PM, Connor Abbott wrote:
>>>> On Thu, May 8, 2025 at 2:14 PM Konrad Dybcio <konradybcio@...nel.org> wrote:
>>>>>
>>>>> From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
>>>>>
>>>>> On A663 (SA8775P) the value matches exactly.
>>>>>
>>>>> On A610, the value matches on SM6115, but is different on SM6125. That
>>>>> turns out not to be a problem, as the bits that differ aren't even
>>>>> interpreted.
>>>>
>>>> This is definitely going to break userspace, because the kernel
>>>> doesn't expose the UBWC version, instead exposing just the swizzle and
>>>> userspace expects that it sets the right value for older UBWC versions
>>>> before it became configurable (0x7 for UBWC 1.0 and 0x6 for 2.0-3.0).
>>>> It looks like the data for SM6125 is just wrong.
>>>
>>> Oh that's sad.. I'll drop this commit
>>
>> Wait uh, we have this data in the common config.. why would it break
>> userspace?
>>
>> Konrad
> 
> As you said in the commit message SM6125 has ubwc_swizzle = 1 which
> seems wrong to me (it should be 7), it just didn't matter before that
> it was wrong. You should probably just fix that.

Oh so you meant that the 6125's value would break userspace - gotcha

Konrad