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

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Message-ID: <CACu1E7EfgPFcSgGA5TkAVqpO=K2G1AjNVbRij60TknCx5PcoqA@mail.gmail.com>
Date: Fri, 9 May 2025 10:48:02 -0400
From: Connor Abbott <cwabbott0@...il.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.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 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.

Connor