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Message-ID: <928822fd-642a-5ca7-7b42-dc7885f3cf51@arm.com>
Date: Thu, 17 Aug 2023 17:35:34 +0100
From: Robin Murphy <robin.murphy@....com>
To: Michael Shavit <mshavit@...gle.com>, iommu@...ts.linux.dev
Cc: Jason Gunthorpe <jgg@...pe.ca>,
Jean-Philippe Brucker <jean-philippe@...aro.org>,
Joerg Roedel <joro@...tes.org>,
Lu Baolu <baolu.lu@...ux.intel.com>,
Nicolin Chen <nicolinc@...dia.com>,
Tomas Krcka <krckatom@...zon.de>,
Will Deacon <will@...nel.org>,
Yicong Yang <yangyicong@...ilicon.com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/arm-smmu-v3: Simplify stage selection logic
On 2023-08-17 17:03, Michael Shavit wrote:
> It is invalid for an arm-smmu-v3 to have neither FEAT_TRANS_S1 nor
> FEAT_TRANS_S2 bits set, and this is even checked in the probe.
>
> Only set ARM_SMMU_DOMAIN_S2 if FEAT_TRANS_S1 isn't supported, otherwise set
> ARM_SMMU_DOMAIN_S1. This is clearer as the existing code implies that
> something more sophisticated is going on with the stage selection logic.
The reason it's like this is because of arm_smmu_enable_nesting(), which
*is* the additional thing that's going on with the stage selection logic.
Thanks,
Robin.
> Signed-off-by: Michael Shavit <mshavit@...gle.com>
> ---
>
> drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index 9b0dc35056019..e74c8c630adfa 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -2206,7 +2206,7 @@ static int arm_smmu_domain_finalise(struct iommu_domain *domain,
> /* Restrict the stage to what we can actually support */
> if (!(smmu->features & ARM_SMMU_FEAT_TRANS_S1))
> smmu_domain->stage = ARM_SMMU_DOMAIN_S2;
> - if (!(smmu->features & ARM_SMMU_FEAT_TRANS_S2))
> + else
> smmu_domain->stage = ARM_SMMU_DOMAIN_S1;
>
> switch (smmu_domain->stage) {
>
> base-commit: 6eaae198076080886b9e7d57f4ae06fa782f90ef
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