linux-kernel - Re: [PATCH 0/5] Qcom smmu-500 TLB invalidation errata for sdm845

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Date:   Tue, 14 Aug 2018 17:54:50 +0530
From:   Vivek Gautam <vivek.gautam@...eaurora.org>
To:     Will Deacon <will.deacon@....com>
Cc:     joro@...tes.org, andy.gross@...aro.org, robin.murphy@....com,
        bjorn.andersson@...aro.org, iommu@...ts.linux-foundation.org,
        mark.rutland@....com, david.brown@...aro.org, tfiga@...omium.org,
        swboyd@...omium.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, robdclark@...il.com
Subject: Re: [PATCH 0/5] Qcom smmu-500 TLB invalidation errata for sdm845

Hi Will,


On 8/14/2018 5:10 PM, Will Deacon wrote:
> Hi Vivek,
>
> On Tue, Aug 14, 2018 at 04:25:23PM +0530, Vivek Gautam wrote:
>> Qcom's implementation of arm,mmu-500 on sdm845 has a functional/performance
>> errata [1] because of which the TCU cache look ups are stalled during
>> invalidation cycle. This is mitigated by serializing all the invalidation
>> requests coming to the smmu.
> How does this implementation differ from the one supported by qcom_iommu.c?
> I notice you're adding firmware hooks here, which we avoided by having the
> extra driver. Please help me understand which devices exist, how they
> differ, and which drivers are intended to support them!

IIRC, the qcom_iommu driver was intended to support the static context 
bank - SID
mapping, and is very specific to the smmu-v2 version present on msm8916 soc.
However, this is the qcom's mmu-500 implementation specific errata. 
qcom_iommu
will not be able to support mmu-500 configurations.
Rob Clark can add more.
Let you know what you suggest.

>
> Also -- you didn't CC all the maintainers for the firmware bits, so adding
> Andy here for that, and Rob for the previous question.

I added Andy to the series, would you want me to add Rob H also?

Best regards
Vivek

>
> Thanks,
>
> Will