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

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Message-ID: <dedbfb2f-012a-404f-87d1-2f3cd04b0e74@oss.qualcomm.com>
Date: Fri, 9 May 2025 15:37:16 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Connor Abbott <cwabbott0@...il.com>,
        Konrad Dybcio <konradybcio@...nel.org>
Cc: 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 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