[PATCH] iommu/arm-smmu: Force identity domains for legacy binding

[Robin Murphy]

When using the legacy "mmu-masters" DT binding, we reject DMA domains
since we have no guarantee of driver probe order and thus can't rely on
client drivers getting the correct DMA ops. However, we can do better
than fall back to the old no-default-domain behaviour now, by forcing an
identity default domain instead. This also means that detaching from a
VFIO domain can actually work - that looks to have been broken for over
6 years, so clearly isn't something that legacy binding users care
about, but we may as well make the driver code make sense anyway.

Suggested-by: Jason Gunthorpe <jgg at nvidia.com>
Signed-off-by: Robin Murphy <robin.murphy at arm.com>
---
 drivers/iommu/arm/arm-smmu/arm-smmu.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c
index 568cce590ccc..e7ec2b74a28d 100644
--- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
+++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
@@ -1574,6 +1574,9 @@ static int arm_smmu_def_domain_type(struct device *dev)
 	struct arm_smmu_master_cfg *cfg = dev_iommu_priv_get(dev);
 	const struct arm_smmu_impl *impl = cfg->smmu->impl;
 
+	if (using_legacy_binding)
+		return IOMMU_DOMAIN_IDENTITY;
+
 	if (impl && impl->def_domain_type)
 		return impl->def_domain_type(dev);
 
-- 
2.35.3.dirty