iommu/virtio: Make instance lookup robust

Much like arm-smmu in commit 7d83513 ("iommu/arm-smmu: Make
instance lookup robust"), virtio-iommu appears to have the same issue
where iommu_device_register() makes the IOMMU instance visible to other
API callers (including itself) straight away, but internally the
instance isn't ready to recognise itself for viommu_probe_device() to
work correctly until after viommu_probe() has returned. This matters a
lot more now that bus_iommu_probe() has the DT/VIOT knowledge to probe
client devices the way that was always intended. Tweak the lookup and
initialisation in much the same way as for arm-smmu, to ensure that what
we register is functional and ready to go.

Cc: stable@vger.kernel.org
Fixes: bcb81ac ("iommu: Get DT/ACPI parsing into the proper probe path")
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Link: https://lore.kernel.org/r/308911aaa1f5be32a3a709996c7bd6cf71d30f33.1755190036.git.robin.murphy@arm.com
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

Author: rmurphy-arm

drivers/iommu/virtio-iommu.c

@@ -998,8 +998,7 @@ static void viommu_get_resv_regions(struct device *dev, struct list_head *head)
 	iommu_dma_get_resv_regions(dev, head);
 }
 
-static const struct iommu_ops viommu_ops;
-static struct virtio_driver virtio_iommu_drv;
+static const struct bus_type *virtio_bus_type;
 
 static int viommu_match_node(struct device *dev, const void *data)
 {
@@ -1008,8 +1007,9 @@ static int viommu_match_node(struct device *dev, const void *data)
 
 static struct viommu_dev *viommu_get_by_fwnode(struct fwnode_handle *fwnode)
 {
-	struct device *dev = driver_find_device(&virtio_iommu_drv.driver, NULL,
-						fwnode, viommu_match_node);
+	struct device *dev = bus_find_device(virtio_bus_type, NULL, fwnode,
+					     viommu_match_node);
+
 	put_device(dev);
 
 	return dev ? dev_to_virtio(dev)->priv : NULL;
@@ -1160,6 +1160,9 @@ static int viommu_probe(struct virtio_device *vdev)
 	if (!viommu)
 		return -ENOMEM;
 
+	/* Borrow this for easy lookups later */
+	virtio_bus_type = dev->bus;
+
 	spin_lock_init(&viommu->request_lock);
 	ida_init(&viommu->domain_ids);
 	viommu->dev = dev;
@@ -1229,10 +1232,10 @@ static int viommu_probe(struct virtio_device *vdev)
 	if (ret)
 		goto err_free_vqs;
 
-	iommu_device_register(&viommu->iommu, &viommu_ops, parent_dev);
-
 	vdev->priv = viommu;
 
+	iommu_device_register(&viommu->iommu, &viommu_ops, parent_dev);
+
 	dev_info(dev, "input address: %u bits\n",
 		 order_base_2(viommu->geometry.aperture_end));
 	dev_info(dev, "page mask: %#llx\n", viommu->pgsize_bitmap);