iommu: Revive device_group iommu-ops call-back

That call-back is currently unused, change it into a
call-back function for finding the right IOMMU group for a
device.
This is a first step to remove the hard-coded PCI dependency
in the iommu-group code.
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/iommu.c

@@ -814,6 +814,7 @@ static struct iommu_group *iommu_group_get_for_pci_dev(struct pci_dev *pdev)
  */
 struct iommu_group *iommu_group_get_for_dev(struct device *dev)
 {
+	const struct iommu_ops *ops = dev->bus->iommu_ops;
 	struct iommu_group *group;
 	int ret;
 
@@ -821,10 +822,12 @@ struct iommu_group *iommu_group_get_for_dev(struct device *dev)
 	if (group)
 		return group;
 
-	if (!dev_is_pci(dev))
-		return ERR_PTR(-EINVAL);
+	group = ERR_PTR(-EINVAL);
 
-	group = iommu_group_get_for_pci_dev(to_pci_dev(dev));
+	if (ops && ops->device_group)
+		group = ops->device_group(dev);
+	else if (dev_is_pci(dev))
+		group = iommu_group_get_for_pci_dev(to_pci_dev(dev));
 
 	if (IS_ERR(group))
 		return group;

include/linux/iommu.h

@@ -168,7 +168,7 @@ struct iommu_ops {
 	phys_addr_t (*iova_to_phys)(struct iommu_domain *domain, dma_addr_t iova);
 	int (*add_device)(struct device *dev);
 	void (*remove_device)(struct device *dev);
-	int (*device_group)(struct device *dev, unsigned int *groupid);
+	struct iommu_group *(*device_group)(struct device *dev);
 	int (*domain_get_attr)(struct iommu_domain *domain,
 			       enum iommu_attr attr, void *data);
 	int (*domain_set_attr)(struct iommu_domain *domain,