iommu/amd: Split IOMMU group allocation and attach

Add a WARN_ON to make it clear why we don't add dma_pdev->dev to the
group we're allocating.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

drivers/iommu/amd_iommu.c

@@ -325,6 +325,24 @@ static struct pci_dev *get_isolation_root(struct pci_dev *pdev)
 	return dma_pdev;
 }
 
+static int use_pdev_iommu_group(struct pci_dev *pdev, struct device *dev)
+{
+	struct iommu_group *group = iommu_group_get(&pdev->dev);
+	int ret;
+
+	if (!group) {
+		group = iommu_group_alloc();
+		if (IS_ERR(group))
+			return PTR_ERR(group);
+
+		WARN_ON(&pdev->dev != dev);
+	}
+
+	ret = iommu_group_add_device(group, dev);
+	iommu_group_put(group);
+	return ret;
+}
+
 static int init_iommu_group(struct device *dev)
 {
 	struct iommu_dev_data *dev_data;
@@ -353,18 +371,8 @@ static int init_iommu_group(struct device *dev)
 		dma_pdev = pci_dev_get(to_pci_dev(dev));
 
 	dma_pdev = get_isolation_root(dma_pdev);
-	group = iommu_group_get(&dma_pdev->dev);
+	ret = use_pdev_iommu_group(dma_pdev, dev);
 	pci_dev_put(dma_pdev);
-	if (!group) {
-		group = iommu_group_alloc();
-		if (IS_ERR(group))
-			return PTR_ERR(group);
-	}
-
-	ret = iommu_group_add_device(group, dev);
-
-	iommu_group_put(group);
-
 	return ret;
 }