iommu: Add DMA mapping operations

In order to support IOMMUs in non-bypass mode we need device ops
to map and unmap DMA memory.  The map operation enters a mapping
for a region specified by CPU address and size into the translation
table of the IOMMU and returns a DMA address suitable for
programming the device to do DMA.  The unmap operation removes
this mapping from the translation table of the IOMMU.

Signed-off-by: Mark Kettenis <kettenis@openbsd.org>

include/dm/device.h

@@ -165,6 +165,7 @@ enum {
  *		automatically when the device is removed / unbound
  * @dma_offset: Offset between the physical address space (CPU's) and the
  *		device's bus address space
+ * @iommu: IOMMU device associated with this device
  */
 struct udevice {
 	const struct driver *driver;
@@ -194,6 +195,9 @@ struct udevice {
 #if CONFIG_IS_ENABLED(DM_DMA)
 	ulong dma_offset;
 #endif
+#if CONFIG_IS_ENABLED(IOMMU)
+	struct udevice *iommu;
+#endif
 };
 
 static inline int dm_udevice_size(void)