linux-kernel - Re: [PATCH v16 1/5] iommu/arm-smmu: re-enable context caching in smmu reset operation

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Message-ID: <9ab96e76-533e-4163-aef5-71a0ca5e82d3@quicinc.com>
Date: Mon, 4 Nov 2024 12:01:12 +0530
From: Bibek Kumar Patro <quic_bibekkum@...cinc.com>
To: Will Deacon <will@...nel.org>
CC: <robdclark@...il.com>, <robin.murphy@....com>, <joro@...tes.org>,
        <jgg@...pe.ca>, <jsnitsel@...hat.com>, <robh@...nel.org>,
        <krzysztof.kozlowski@...aro.org>, <quic_c_gdjako@...cinc.com>,
        <dmitry.baryshkov@...aro.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>
Subject: Re: [PATCH v16 1/5] iommu/arm-smmu: re-enable context caching in smmu
 reset operation



On 11/1/2024 5:40 PM, Will Deacon wrote:
> On Wed, Oct 30, 2024 at 05:00:13PM +0530, Bibek Kumar Patro wrote:
>> On 10/29/2024 6:17 PM, Will Deacon wrote:
>>> On Fri, Oct 25, 2024 at 07:51:22PM +0530, Bibek Kumar Patro wrote:
>>>> On 10/24/2024 6:22 PM, Will Deacon wrote:
>>>>> On Tue, Oct 08, 2024 at 06:24:06PM +0530, Bibek Kumar Patro wrote:
>>> If you want to gate the errata workarounds on policy, then please follow
>>> what we do for the CPU: add a Kconfig option (e.g.
>>> ARM_SMMU_WORKAROUND_BROKEN_CPRE) which defaults to "on" (assuming that
>>> the relevant errata aren't all "rare") and update silicon-errata.rst
>>> accordingly.
>>>
>>> Then you can choose to disable them in your .config if you're happy to
>>> pick up the pieces.
>>
>> This seems to be a good idea to me . I am thinking of this approach based on
>> your suggestion,
>> i.e. we can bind the original workaround in
>> arm_mmu500_reset implementation within ARM_SMMU_WORKAROUND_BROKEN_CPRE
>> config (defualts to on, CPRE would be disabled) and in QCOM SoCs default it
>> to off
>> (when ARM_SMMU_QCOM=Y -> switch ARM_SMMU_WORKAROUND_BROKEN_CPRE=N).
> 
> ARM_SMMU_QCOM is enabled by default, so please don't do that. People who
> want to disable errata workarounds based on a hunch can do that themselves.
> There's no need to try to do that automatically in Kconfig.
> 

Okay I see, that seems better. To allow users to manually toggle the 
config switch for
disabling errata workarounds based on their specific needs,
rather than having it enabled by default.

>> In silicon-errata.rst would updating ARM_SMMU_WORKAROUND_BROKEN_CPRE be okay
>> , as the config names are based on erratum number.
> 
> In this case, the Kconfig option covers a variety of errata so how about
> we go with:
> 
> 	ARM_SMMU_MMU_500_CPRE_ERRATA
> 
> and then you can list all of the numbers in the "Erratum ID" column?
> 

Ack, this name sounds self-explanatory to me. Thanks for the suggestion,
I'll proceed with this name and ensure documenting the known numbers in 
Erratum ID column
<#826419, #841119, #562869, #1047329>

Thanks & regards,
Bibek


> Will
>