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

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Message-ID: <20241101121024.GC8518@willie-the-truck>
Date: Fri, 1 Nov 2024 12:10:25 +0000
From: Will Deacon <will@...nel.org>
To: Bibek Kumar Patro <quic_bibekkum@...cinc.com>
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 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.

> 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?

Will