iommu: Introduce a callback to struct iommu_resv_region

A callback is introduced to struct iommu_resv_region to free memory
allocations associated with the reserved region. This will be useful
when we introduce support for IORT RMR based reserved regions.
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Tested-by: NSteven Price <steven.price@arm.com>
Tested-by: NLaurentiu Tudor <laurentiu.tudor@nxp.com>
Tested-by: NHanjun Guo <guohanjun@huawei.com>
Signed-off-by: NShameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Acked-by: NRobin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/20220615101044.1972-2-shameerali.kolothum.thodi@huawei.comSigned-off-by: NJoerg Roedel <jroedel@suse.de>

drivers/iommu/iommu.c

@@ -2590,16 +2590,22 @@ void iommu_put_resv_regions(struct device *dev, struct list_head *list)
  * @list: reserved region list for device
  *
  * IOMMU drivers can use this to implement their .put_resv_regions() callback
- * for simple reservations. Memory allocated for each reserved region will be
- * freed. If an IOMMU driver allocates additional resources per region, it is
- * going to have to implement a custom callback.
+ * for simple reservations. If a per region callback is provided that will be
+ * used to free all memory allocations associated with the reserved region or
+ * else just free up the memory for the regions. If an IOMMU driver allocates
+ * additional resources per region, it is going to have to implement a custom
+ * callback.
  */
 void generic_iommu_put_resv_regions(struct device *dev, struct list_head *list)
 {
 	struct iommu_resv_region *entry, *next;
 
-	list_for_each_entry_safe(entry, next, list, list)
-		kfree(entry);
+	list_for_each_entry_safe(entry, next, list, list) {
+		if (entry->free)
+			entry->free(dev, entry);
+		else
+			kfree(entry);
+	}
 }
 EXPORT_SYMBOL(generic_iommu_put_resv_regions);
 

include/linux/iommu.h

@@ -135,6 +135,7 @@ enum iommu_resv_type {
  * @length: Length of the region in bytes
  * @prot: IOMMU Protection flags (READ/WRITE/...)
  * @type: Type of the reserved region
+ * @free: Callback to free associated memory allocations
  */
 struct iommu_resv_region {
 	struct list_head	list;
@@ -142,6 +143,7 @@ struct iommu_resv_region {
 	size_t			length;
 	int			prot;
 	enum iommu_resv_type	type;
+	void (*free)(struct device *dev, struct iommu_resv_region *region);
 };
 
 /**