iommu/arm-smmu: Report IOMMU_CAP_CACHE_COHERENCY better

Assuming that any SMMU can enforce coherency for any device is clearly
nonsense. Although technically even a single SMMU instance can be wired
up to only be capable of emitting coherent traffic for some of the
devices it translates, it's a fairly realistic approximation that if the
SMMU's pagetable walker is wired up to a coherent interconnect then all
its translation units probably are too, and conversely that lack of
coherent table walks implies a non-coherent system in general. Either
way it's still less inaccurate than what we've been claiming so far.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/106c9741415f0b6358c72d53ae9c78c553a2b45c.1660574547.git.robin.murphy@arm.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

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 ab919ec..fceab59 100644 (file)
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -1994,9 +1994,12 @@ static const struct iommu_flush_ops arm_smmu_flush_ops = {
 /* IOMMU API */
 static bool arm_smmu_capable(struct device *dev, enum iommu_cap cap)
 {
+       struct arm_smmu_master *master = dev_iommu_priv_get(dev);
+
        switch (cap) {
        case IOMMU_CAP_CACHE_COHERENCY:
-               return true;
+               /* Assume that a coherent TCU implies coherent TBUs */
+               return master->smmu->features & ARM_SMMU_FEAT_COHERENCY;
        case IOMMU_CAP_NOEXEC:
                return true;
        default:

diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c
index ce036a0..8039c8b 100644 (file)
--- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
+++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
@@ -1332,13 +1332,12 @@ static phys_addr_t arm_smmu_iova_to_phys(struct iommu_domain *domain,
 
 static bool arm_smmu_capable(struct device *dev, enum iommu_cap cap)
 {
+       struct arm_smmu_master_cfg *cfg = dev_iommu_priv_get(dev);
+
        switch (cap) {
        case IOMMU_CAP_CACHE_COHERENCY:
-               /*
-                * Return true here as the SMMU can always send out coherent
-                * requests.
-                */
-               return true;
+               /* Assume that a coherent TCU implies coherent TBUs */
+               return cfg->smmu->features & ARM_SMMU_FEAT_COHERENT_WALK;
        case IOMMU_CAP_NOEXEC:
                return true;
        default: