iommu/arm-smmu-v3: Fail aliasing StreamIDs more gracefully

commit 2d00c34
Author: Robin Murphy <[email protected]>
Date: Fri Apr 11 15:09:14 2025 +0100

    iommu/arm-smmu-v3: Fail aliasing StreamIDs more gracefully

    We've never supported StreamID aliasing between devices, and as such
    they will never have had functioning DMA, but this is not fatal to the
    SMMU itself. Although aliasing between hard-wired platform device
    StreamIDs would tend to raise questions about the whole system, in
    practice it's far more likely to occur relatively innocently due to
    legacy PCI bridges, where the underlying StreamID mappings are still
    perfectly reasonable.

    As such, return a more benign -ENODEV when failing probe for such an
    unsupported device (and log a more obvious error message), so that it
    doesn't break the entire SMMU probe now that bus_iommu_probe() runs in
    the right order and can propagate that error back. The end result is
    still that the device doesn't get an IOMMU group and probably won't
    work, same as before.

    Signed-off-by: Robin Murphy <[email protected]>
    Link: https://lore.kernel.org/r/39d54e49c8476efc4653e352150d44b185d6d50f.1744380554.git.robin.murphy@arm.com
    Signed-off-by: Will Deacon <[email protected]>

(cherry picked from commit 2d00c34)
Signed-off-by: Jerry Snitselaar <[email protected]>
Upstream-Status: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
JIRA: https://issues.redhat.com/browse/RHEL-89891

Author: snits

drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c

@@ -3411,9 +3411,9 @@ static int arm_smmu_insert_master(struct arm_smmu_device *smmu,
 				continue;
 
 			dev_warn(master->dev,
-				 "stream %u already in tree from dev %s\n", sid,
-				 dev_name(existing_master->dev));
-			ret = -EINVAL;
+				 "Aliasing StreamID 0x%x (from %s) unsupported, expect DMA to be broken\n",
+				 sid, dev_name(existing_master->dev));
+			ret = -ENODEV;
 			break;
 		}
 	}