iommu: Introduce domain_alloc and domain_free iommu_ops

These new call-backs defer the allocation and destruction of
'struct iommu_domain' to the iommu driver. This allows
drivers to embed this struct into their private domain
structures and to get rid of the domain_init and
domain_destroy call-backs when all drivers have been
converted.
Tested-by: NThierry Reding <treding@nvidia.com>
Tested-by: NHeiko Stuebner <heiko@sntech.de>
Reviewed-by: NAlex Williamson <alex.williamson@redhat.com>
Acked-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NJoerg Roedel <jroedel@suse.de>

drivers/iommu/iommu.c

@@ -900,25 +900,33 @@ EXPORT_SYMBOL_GPL(iommu_set_fault_handler);
 
 struct iommu_domain *iommu_domain_alloc(struct bus_type *bus)
 {
+	const struct iommu_ops *ops;
 	struct iommu_domain *domain;
-	int ret;
 
 	if (bus == NULL || bus->iommu_ops == NULL)
 		return NULL;
 
+	ops = bus->iommu_ops;
+
+	if (ops->domain_alloc)
+		domain = ops->domain_alloc();
+	else
 		domain = kzalloc(sizeof(*domain), GFP_KERNEL);
+
 	if (!domain)
 		return NULL;
 
 	domain->ops = bus->iommu_ops;
 
-	ret = domain->ops->domain_init(domain);
-	if (ret)
+	if (ops->domain_init && domain->ops->domain_init(domain))
 		goto out_free;
 
 	return domain;
 
 out_free:
+	if (ops->domain_free)
+		ops->domain_free(domain);
+	else
 		kfree(domain);
 
 	return NULL;
@@ -927,9 +935,14 @@ EXPORT_SYMBOL_GPL(iommu_domain_alloc);
 
 void iommu_domain_free(struct iommu_domain *domain)
 {
-	if (likely(domain->ops->domain_destroy != NULL))
-		domain->ops->domain_destroy(domain);
+	const struct iommu_ops *ops = domain->ops;
 
+	if (likely(ops->domain_destroy != NULL))
+		ops->domain_destroy(domain);
+
+	if (ops->domain_free)
+		ops->domain_free(domain);
+	else
 		kfree(domain);
 }
 EXPORT_SYMBOL_GPL(iommu_domain_free);

include/linux/iommu.h

@@ -115,6 +115,11 @@ struct iommu_ops {
 	bool (*capable)(enum iommu_cap);
 	int (*domain_init)(struct iommu_domain *domain);
 	void (*domain_destroy)(struct iommu_domain *domain);
+
+	/* Domain allocation and freeing by the iommu driver */
+	struct iommu_domain *(*domain_alloc)(void);
+	void (*domain_free)(struct iommu_domain *);
+
 	int (*attach_dev)(struct iommu_domain *domain, struct device *dev);
 	void (*detach_dev)(struct iommu_domain *domain, struct device *dev);
 	int (*map)(struct iommu_domain *domain, unsigned long iova,