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iommu/arm-smmu-v3: Explain why ATS stays disabled with bypass

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The SMMU does not support enabling ATS for a bypass stream. Add a comment.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Link: https://lore.kernel.org/r/20230321100559.341981-1-jean-philippe@linaro.org
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Jean-Philippe Brucker
2023-03-21 10:06:00 +00:00
committed by Will Deacon
parent e8d018dd02
commit 8c153645fa
1 changed files with 7 additions and 0 deletions
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7
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
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@@ -2447,6 +2447,13 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
master->domain = smmu_domain;
/*
* The SMMU does not support enabling ATS with bypass. When the STE is
* in bypass (STE.Config[2:0] == 0b100), ATS Translation Requests and
* Translated transactions are denied as though ATS is disabled for the
* stream (STE.EATS == 0b00), causing F_BAD_ATS_TREQ and
* F_TRANSL_FORBIDDEN events (IHI0070Ea 5.2 Stream Table Entry).
*/
if (smmu_domain->stage != ARM_SMMU_DOMAIN_BYPASS)
master->ats_enabled = arm_smmu_ats_supported(master);