linux-kernel - Re: [PATCH] iommu/arm-smmu-qcom: Work around SDM845 Adreno SMMU w/ 16K pages

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Message-ID: <CAF6AEGvd6a4a2Wbm_D2mhg+i7bapDadgnaOQZU7m68uA8SS5Jw@mail.gmail.com>
Date: Fri, 23 Aug 2024 10:15:00 -0700
From: Rob Clark <robdclark@...il.com>
To: Will Deacon <will@...nel.org>
Cc: Trilok Soni <quic_tsoni@...cinc.com>, Dmitry Baryshkov <dmitry.baryshkov@...aro.org>, 
	Konrad Dybcio <konradybcio@...il.com>, Konrad Dybcio <konradybcio@...nel.org>, 
	Bjorn Andersson <andersson@...nel.org>, Robin Murphy <robin.murphy@....com>, 
	Joerg Roedel <joro@...tes.org>, Marijn Suijten <marijn.suijten@...ainline.org>, iommu@...ts.linux.dev, 
	linux-arm-msm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, Konrad Dybcio <konrad.dybcio@...aro.org>, 
	Sumit Semwal <sumit.semwal@...aro.org>
Subject: Re: [PATCH] iommu/arm-smmu-qcom: Work around SDM845 Adreno SMMU w/
 16K pages

On Fri, Aug 23, 2024 at 8:21 AM Will Deacon <will@...nel.org> wrote:
>
> On Tue, Jul 30, 2024 at 10:16:00AM -0700, Trilok Soni wrote:
> > On 7/30/2024 1:50 AM, Dmitry Baryshkov wrote:
> > >>>>>> SDM845's Adreno SMMU is unique in that it actually advertizes support
> > >>>>>> for 16K (and 32M) pages, which doesn't hold for newer SoCs.
> > > My question is about forbidding 16k pages for sdm845 only or for other
> > > chips too. I'd assume that it shouldn't also work for other smmu-v2
> > > platforms.
> >
> > Yes, my understanding was that SMMUv2 based IPs doesn't have 16k support
> > and it is only starting from SMMUv3.
>
> I'm not sure about that. The architecture doc for SMMUv2 talks about the
> AArch64 translation regime in section 1.5 and bit 13 of SMMU_IDR2 says:
>
>   | PTFSv8_16kB, bit[13]
>   | Support for 16KB translation granule size. The possible values of this bit are:
>   | 0   The 16KB translation granule is not supported.
>   | 1   The 16KB translation granule is supported.
>   | In SMMUv1, this bit is reserved.
>
> so I think Konrad's patch is about right, but if you want to extend it
> to cover other implementations then that's fine too.
>

Perhaps that should have been "qcom's SMMUv2 based IPs doesn't have
16k support"?

At any rate, 16k sizes don't appear to work on sc7180 as well.  I
don't really have any other data points but it wouldn't really
surprise me if this applied to all qc smmu-v2

BR,
-R