linux-kernel - Re: [PATCH RFT 07/14] drm/msm/a6xx: Resolve the meaning of UBWC

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Message-ID: <b374b468-819b-4f5a-9ecc-0926c3696db3@oss.qualcomm.com>
Date: Fri, 9 May 2025 14:39:42 +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 07/14] drm/msm/a6xx: Resolve the meaning of UBWC_MODE

On 5/9/25 2:37 PM, Konrad Dybcio wrote:
> On 5/8/25 8:25 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>
>>>
>>> This bit is set iff the UBWC version is 1.0. That notably does not
>>> include QCM2290's "no UBWC".
>>
>> While this is technically true, AFAIK the only difference between UBWC
>> 1.0 and 2.0 is that newer UBWC disables level 1 bank swizzling, which
>> is why I originally wrote it this way. There's a bit of redundancy
>> between the UBWC version and ubwc_swizzle bit 0.
> 
> It turns out to be a hardware matter

Well you just said that.. in any case, i can do either (or both with a
sanity check)

Konrad