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

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Message-ID: <3ac669af-a68e-874f-4c3e-91a2e9f676af@codeaurora.org>
Date:   Wed, 5 Sep 2018 16:55:22 +0530
From:   Vivek Gautam <vivek.gautam@...eaurora.org>
To:     Rob Clark <robdclark@...il.com>
Cc:     Will Deacon <will.deacon@....com>,
        "list@....net:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        Joerg Roedel <joro@...tes.org>, joro@...tes.org,
        Andy Gross <andy.gross@...aro.org>,
        Robin Murphy <robin.murphy@....com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        "list@....net:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org,
        Mark Rutland <mark.rutland@....com>,
        David Brown <david.brown@...aro.org>,
        Tomasz Figa <tfiga@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 0/5] Qcom smmu-500 TLB invalidation errata for sdm845



On 9/5/2018 3:34 PM, Rob Clark wrote:
> On Wed, Sep 5, 2018 at 5:22 AM Vivek Gautam <vivek.gautam@...eaurora.org> wrote:
>>
>> On 8/14/2018 5:54 PM, Vivek Gautam wrote:
>>> 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.
>> Rob, can you please comment about how qcom-smmu driver has different
>> implementation
>> from arm-smmu driver?
> sorry, I missed this thread earlier.  But yeah, as you mentioned, the
> purpose for qcom_iommu.c was to deal with the static context/SID
> mapping.
>
> (I guess it is all just software, and we could make qcom_iommu.c
> support dynamic mapping as well, but I think then it starts to
> duplicate most of arm_smmu.c, so that doesn't seem like the right
> direction)

Thanks Rob for the response. I will wait for Will's response on how would he
like this support be implemented.

Best regards
Vivek
>
> BR,
> -R
>
>> Will, in case we would want to use arm-smmu driver, what would you
>> suggest for
>> having the firmware hooks?
>> Thanks.
>>
>> Best regards
>> Vivek