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Robin Murphy authored
Although it's vanishingly unlikely that anyone would integrate an SMMU within a coherent interconnect without also making the pagetable walk interface coherent, the same effect happens if a coherent SMMU fails to advertise CTTW correctly. This turns out to be the case on some popular NXP SoCs, where VFIO started failing the IOMMU_CAP_CACHE_COHERENCY test, even though IOMMU_CACHE *was* previously achieving the desired effect anyway thanks to the underlying integration. While those SoCs stand to gain some more general benefits from a firmware update to override CTTW correctly in DT/ACPI, it's also easy to work around this in Linux as well, to avoid imposing too much on affected users - since the upstream client devices *are* correctly marked as coherent, we can trivially infer their coherent paths through the SMMU as well. Reported-by:
Vladimir Oltean <vladimir.oltean@nxp.com> Fixes: df198b37 ("iommu/arm-smmu: Report IOMMU_CAP_CACHE_COHERENCY better") Signed-off-by:
Robin Murphy <robin.murphy@arm.com> Tested-by:
Vladimir Oltean <vladimir.oltean@nxp.com> Link: https://lore.kernel.org/r/d6dc41952961e5c7b21acac08a8bf1eb0f69e124.1671123115.git.robin.murphy@arm.comSigned-off-by:
Will Deacon <will@kernel.org>
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