powerpc: Change archdata dma_data to a union

Sometimes this is used to hold a simple offset, and sometimes
it is used to hold a pointer.  This patch changes it to a union containing
void * and dma_addr_t.  get/set accessors are also provided, because it was
getting a bit ugly to get to the actual data.

Signed-off-by: Becky Bruce <beckyb@kernel.crashing.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/include/asm/device.h b/arch/powerpc/include/asm/device.h
index 9dade15..6d94d27 100644
--- a/arch/powerpc/include/asm/device.h
+++ b/arch/powerpc/include/asm/device.h
@@ -15,7 +15,16 @@
 
 	/* DMA operations on that device */
 	struct dma_map_ops	*dma_ops;
-	void			*dma_data;
+
+	/*
+	 * When an iommu is in use, dma_data is used as a ptr to the base of the
+	 * iommu_table.  Otherwise, it is a simple numerical offset.
+	 */
+	union {
+		dma_addr_t	dma_offset;
+		void		*iommu_table_base;
+	} dma_data;
+
 #ifdef CONFIG_SWIOTLB
 	dma_addr_t		max_direct_dma_addr;
 #endif