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Subject: Re: [PATCH 0/5] Qcom smmu-500 TLB invalidation errata for sdm845
From:   Vivek Gautam <vivek.gautam@codeaurora.org>
To:     Will Deacon <will.deacon@arm.com>, robdclark@gmail.com
Cc:     joro@8bytes.org, andy.gross@linaro.org, robin.murphy@arm.com,
        bjorn.andersson@linaro.org, iommu@lists.linux-foundation.org,
        mark.rutland@arm.com, david.brown@linaro.org, tfiga@chromium.org,
        swboyd@chromium.org, linux-kernel@vger.kernel.org,
        linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org
References: <20180814105528.20592-1-vivek.gautam@codeaurora.org>
 <20180814114009.GF28664@arm.com>
 <ad4e9f85-ff57-ad26-fb25-7b4c08683a52@codeaurora.org>
Message-ID: <3f74124c-b09f-a92d-117d-a747d33a4561@codeaurora.org>
Date:   Wed, 5 Sep 2018 14:52:21 +0530
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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?
Will, in case we would want to use arm-smmu driver, what would you 
suggest for
having the firmware hooks?
Thanks.

Best regards
Vivek
>
>>
>> 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
>