[PATCH 1/2] iommu/arm-smmu: Don't inadvertently reject multiple SMMUv3s

[Robin Murphy]

We now delay installing our per-bus iommu_ops until we know an SMMU has
successfully probed, as they don't serve much purpose beforehand, and
doing so also avoids fights between multiple IOMMU drivers in a single
kernel. However, the upshot of passing the return value of bus_set_iommu()
back from our probe function is that if there happens to be more than
one SMMUv3 device in a system, the second and subsequent probes will
wind up returning -EBUSY to the driver core and getting torn down again.

There are essentially 3 cases in which bus_set_iommu() returns nonzero:
1. The bus already has iommu_ops installed
2. One of the add_device callbacks from the initial notifier failed
3. Allocating or installing the notifier itself failed

The first two are down to devices other than the SMMU in question, so
shouldn't abort an otherwise-successful SMMU probe, whilst the third is
indicative of the kind of catastrophic system failure which isn't going
to get much further anyway. Consequently, there is little harm in
ignoring the return value either way.

CC: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
Signed-off-by: Robin Murphy <robin.murphy at arm.com>
---
 drivers/iommu/arm-smmu-v3.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 15c01c3cd540..74fbef384deb 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -2637,16 +2637,13 @@ static int arm_smmu_device_dt_probe(struct platform_device *pdev)
 	of_iommu_set_ops(dev->of_node, &arm_smmu_ops);
 #ifdef CONFIG_PCI
 	pci_request_acs();
-	ret = bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
-	if (ret)
-		return ret;
+	bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
 #endif
 #ifdef CONFIG_ARM_AMBA
-	ret = bus_set_iommu(&amba_bustype, &arm_smmu_ops);
-	if (ret)
-		return ret;
+	bus_set_iommu(&amba_bustype, &arm_smmu_ops);
 #endif
-	return bus_set_iommu(&platform_bus_type, &arm_smmu_ops);
+	bus_set_iommu(&platform_bus_type, &arm_smmu_ops);
+	return 0;
 }
 
 static int arm_smmu_device_remove(struct platform_device *pdev)
-- 
1.9.1