iommu/arm-smmu: Make instance lookup robust

Relying on the driver list was a cute idea for minimising the scope of
our SMMU device lookups, however it turns out to have a subtle flaw. The
SMMU device only gets added to that list after arm_smmu_device_probe()
returns success, so there's actually no way the iommu_device_register()
call from there could ever work as intended, even if it wasn't already
hampered by the fwspec setup not happening early enough.

Switch both arm_smmu_get_by_fwnode() implementations to use a platform
bus lookup instead, which *will* reliably work. Also make sure that we
don't register SMMUv2 instances until we've fully initialised them, to
avoid similar consequences of the lookup now finding a device with no
drvdata. Moving the error returns is also a perfect excuse to streamline
them with dev_err_probe() in the process.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/6d7ce1dc31873abdb75c895fb8bd2097cce098b4.1733406914.git.robin.murphy@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

Author: rmurphy-arm

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

@@ -3351,8 +3351,8 @@ static struct platform_driver arm_smmu_driver;
 static
 struct arm_smmu_device *arm_smmu_get_by_fwnode(struct fwnode_handle *fwnode)
 {
-	struct device *dev = driver_find_device_by_fwnode(&arm_smmu_driver.driver,
-							  fwnode);
+	struct device *dev = bus_find_device_by_fwnode(&platform_bus_type, fwnode);
+
 	put_device(dev);
 	return dev ? dev_get_drvdata(dev) : NULL;
 }

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

@@ -1411,8 +1411,8 @@ static bool arm_smmu_capable(struct device *dev, enum iommu_cap cap)
 static
 struct arm_smmu_device *arm_smmu_get_by_fwnode(struct fwnode_handle *fwnode)
 {
-	struct device *dev = driver_find_device_by_fwnode(&arm_smmu_driver.driver,
-							  fwnode);
+	struct device *dev = bus_find_device_by_fwnode(&platform_bus_type, fwnode);
+
 	put_device(dev);
 	return dev ? dev_get_drvdata(dev) : NULL;
 }
@@ -2227,29 +2227,26 @@ static int arm_smmu_device_probe(struct platform_device *pdev)
 					i, irq);
 	}
 
+	platform_set_drvdata(pdev, smmu);
+
+	/* Check for RMRs and install bypass SMRs if any */
+	arm_smmu_rmr_install_bypass_smr(smmu);
+
+	arm_smmu_device_reset(smmu);
+	arm_smmu_test_smr_masks(smmu);
+
 	err = iommu_device_sysfs_add(&smmu->iommu, smmu->dev, NULL,
 				     "smmu.%pa", &smmu->ioaddr);
-	if (err) {
-		dev_err(dev, "Failed to register iommu in sysfs\n");
-		return err;
-	}
+	if (err)
+		return dev_err_probe(dev, err, "Failed to register iommu in sysfs\n");
 
 	err = iommu_device_register(&smmu->iommu, &arm_smmu_ops,
 				    using_legacy_binding ? NULL : dev);
 	if (err) {
-		dev_err(dev, "Failed to register iommu\n");
 		iommu_device_sysfs_remove(&smmu->iommu);
-		return err;
+		return dev_err_probe(dev, err, "Failed to register iommu\n");
 	}
 
-	platform_set_drvdata(pdev, smmu);
-
-	/* Check for RMRs and install bypass SMRs if any */
-	arm_smmu_rmr_install_bypass_smr(smmu);
-
-	arm_smmu_device_reset(smmu);
-	arm_smmu_test_smr_masks(smmu);
-
 	/*
 	 * We want to avoid touching dev->power.lock in fastpaths unless
 	 * it's really going to do something useful - pm_runtime_enabled()