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iommu/arm-smmu: Report IOMMU_CAP_CACHE_COHERENCY even betterer

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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: df198b37e7 ("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.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Robin Murphy 2022-12-15 16:51:55 +00:00 committed by Joerg Roedel
parent b7bfaa761d
commit ac9c5e92dd
1 changed files with 8 additions and 2 deletions
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10
drivers/iommu/arm/arm-smmu/arm-smmu.c
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@ -1316,8 +1316,14 @@ static bool arm_smmu_capable(struct device *dev, enum iommu_cap cap)
switch (cap) {
case IOMMU_CAP_CACHE_COHERENCY:
/* Assume that a coherent TCU implies coherent TBUs */
return cfg->smmu->features & ARM_SMMU_FEAT_COHERENT_WALK;
/*
* It's overwhelmingly the case in practice that when the pagetable
* walk interface is connected to a coherent interconnect, all the
* translation interfaces are too. Furthermore if the device is
* natively coherent, then its translation interface must also be.
*/
return cfg->smmu->features & ARM_SMMU_FEAT_COHERENT_WALK ||
device_get_dma_attr(dev) == DEV_DMA_COHERENT;
case IOMMU_CAP_NOEXEC:
return true;
default: