linux-kernel - Re: [PATCH 10/17] drm/msm/a6xx: Rebase GMU register offsets

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Message-ID: <eicw5g5ozli6tvcsvxdorvd5ymxizidodbrfitqezcezwlzdli@6koxrgnu2lj3>
Date: Thu, 2 Oct 2025 04:03:43 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Akhil P Oommen <akhilpo@....qualcomm.com>
Cc: Rob Clark <robin.clark@....qualcomm.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, Sean Paul <sean@...rly.run>,
        Dmitry Baryshkov <lumag@...nel.org>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Jessica Zhang <jessica.zhang@....qualcomm.com>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Jonathan Marek <jonathan@...ek.ca>,
        Jordan Crouse <jordan@...micpenguin.net>,
        Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux.dev, devicetree@...r.kernel.org
Subject: Re: [PATCH 10/17] drm/msm/a6xx: Rebase GMU register offsets

On Thu, Oct 02, 2025 at 02:52:35AM +0530, Akhil P Oommen wrote:
> 
> 
> On 9/30/2025 12:53 PM, Dmitry Baryshkov wrote:
> > On Tue, Sep 30, 2025 at 11:18:15AM +0530, Akhil P Oommen wrote:
> > > GMU registers are always at a fixed offset from the GPU base address,
> > > a consistency maintained at least within a given architecture generation.
> > > In A8x family, the base address of the GMU has changed, but the offsets
> > > of the gmu registers remain largely the same. To enable reuse of the gmu
> > 
> > I understand the code, but I think I'd very much prefer to see it in the
> > catalog file (with the note on how to calculate it). Reading resources
> > for two different devices sounds too strange to be nice. This way you
> > can keep the offsets for a6xx / a7xx untouched and just add the non-zero
> > offset for a8xx.
> 
> It is not clear to me whether the concern is about the calculation part or
> the xml update part.
> 
> If it is about the former,I think it is okay as we have confidence on the
> layout of both devices. They are not random platform devices.

I'd say, the uncertainity that in future the offset will be the same. As
such, it's much easier (in my opinion) to introduce the variable offset
now.

> Also, we may
> have to do something similar for other gpu/gmu reg ranges too to
> conveniently collect a full coredump.

Don't we collect the full GMU register dump?

> 
> -Akhil
> 
> > 
> > > code for A8x chipsets, update the gmu register offsets to be relative
> > > to the GPU's base address instead of GMU's.
> > > 
> > > Signed-off-by: Akhil P Oommen <akhilpo@....qualcomm.com>
> > > ---
> > >   drivers/gpu/drm/msm/adreno/a6xx_gmu.c             |  44 +++-
> > >   drivers/gpu/drm/msm/adreno/a6xx_gmu.h             |  20 +-
> > >   drivers/gpu/drm/msm/registers/adreno/a6xx_gmu.xml | 248 +++++++++++-----------
> > >   3 files changed, 172 insertions(+), 140 deletions(-)
> > 
> 

-- 
With best wishes
Dmitry