iommu: Introduce iommu_request_dm_for_dev()

This function can be called by an IOMMU driver to request
that a device's default domain is direct mapped.
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/iommu.c

@@ -1538,3 +1538,56 @@ void iommu_put_dm_regions(struct device *dev, struct list_head *list)
 	if (ops && ops->put_dm_regions)
 		ops->put_dm_regions(dev, list);
 }
+
+/* Request that a device is direct mapped by the IOMMU */
+int iommu_request_dm_for_dev(struct device *dev)
+{
+	struct iommu_domain *dm_domain;
+	struct iommu_group *group;
+	int ret;
+
+	/* Device must already be in a group before calling this function */
+	group = iommu_group_get_for_dev(dev);
+	if (!group)
+		return -EINVAL;
+
+	mutex_lock(&group->mutex);
+
+	/* Check if the default domain is already direct mapped */
+	ret = 0;
+	if (group->default_domain &&
+	    group->default_domain->type == IOMMU_DOMAIN_IDENTITY)
+		goto out;
+
+	/* Don't change mappings of existing devices */
+	ret = -EBUSY;
+	if (iommu_group_device_count(group) != 1)
+		goto out;
+
+	/* Allocate a direct mapped domain */
+	ret = -ENOMEM;
+	dm_domain = __iommu_domain_alloc(dev->bus, IOMMU_DOMAIN_IDENTITY);
+	if (!dm_domain)
+		goto out;
+
+	/* Attach the device to the domain */
+	ret = __iommu_attach_group(dm_domain, group);
+	if (ret) {
+		iommu_domain_free(dm_domain);
+		goto out;
+	}
+
+	/* Make the direct mapped domain the default for this group */
+	if (group->default_domain)
+		iommu_domain_free(group->default_domain);
+	group->default_domain = dm_domain;
+
+	pr_info("Using direct mapping for device %s\n", dev_name(dev));
+
+	ret = 0;
+out:
+	mutex_unlock(&group->mutex);
+	iommu_group_put(group);
+
+	return ret;
+}

include/linux/iommu.h

@@ -225,6 +225,7 @@ extern void iommu_set_fault_handler(struct iommu_domain *domain,
 
 extern void iommu_get_dm_regions(struct device *dev, struct list_head *list);
 extern void iommu_put_dm_regions(struct device *dev, struct list_head *list);
+extern int iommu_request_dm_for_dev(struct device *dev);
 
 extern int iommu_attach_group(struct iommu_domain *domain,
 			      struct iommu_group *group);
@@ -411,6 +412,11 @@ static inline void iommu_put_dm_regions(struct device *dev,
 {
 }
 
+static inline int iommu_request_dm_for_dev(struct device *dev)
+{
+	return -ENODEV;
+}
+
 static inline int iommu_attach_group(struct iommu_domain *domain,
 				     struct iommu_group *group)
 {