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SubjectRe: [PATCH] iommu/arm-smmu-v3: Simplify stage selection logic
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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@google.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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