iommu: Add function to query the default domain of a group

This will be used to handle unity mappings in the iommu
drivers.
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/iommu.c

@@ -837,6 +837,11 @@ struct iommu_group *iommu_group_get_for_dev(struct device *dev)
 	return group;
 }
 
+struct iommu_domain *iommu_group_default_domain(struct iommu_group *group)
+{
+	return group->default_domain;
+}
+
 static int add_iommu_group(struct device *dev, void *data)
 {
 	struct iommu_callback_data *cb = data;

include/linux/iommu.h

@@ -249,6 +249,7 @@ extern int iommu_group_unregister_notifier(struct iommu_group *group,
 					   struct notifier_block *nb);
 extern int iommu_group_id(struct iommu_group *group);
 extern struct iommu_group *iommu_group_get_for_dev(struct device *dev);
+extern struct iommu_domain *iommu_group_default_domain(struct iommu_group *);
 
 extern int iommu_domain_get_attr(struct iommu_domain *domain, enum iommu_attr,
 				 void *data);