[IA64] fallback to swiotlb for consistent DMA mappings

Patch supplied by Suresh Siddha

This is mainly needed for EM64T platforms and makes sense for ia64 too.
Need of this was broughtup sometime(long time?) back on lkml.
http://www.ussg.iu.edu/hypermail/linux/kernel/0406.3/0112.htmlSigned-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/lib/swiotlb.c

@@ -305,8 +305,15 @@ swiotlb_alloc_coherent (struct device *hwdev, size_t size, dma_addr_t *dma_handl
 	flags |= GFP_DMA;
 
 	ret = (void *)__get_free_pages(flags, get_order(size));
-	if (!ret)
-		return NULL;
+	if (!ret) {
+		 /* DMA_FROM_DEVICE is to avoid the memcpy in map_single */
+		dma_addr_t handle;
+		handle = swiotlb_map_single(NULL, NULL, size, DMA_FROM_DEVICE);
+		if (dma_mapping_error(handle))
+			return NULL;
+
+		ret = phys_to_virt(handle);
+	}
 
 	memset(ret, 0, size);
 	dev_addr = virt_to_phys(ret);
@@ -319,7 +326,12 @@ swiotlb_alloc_coherent (struct device *hwdev, size_t size, dma_addr_t *dma_handl
 void
 swiotlb_free_coherent (struct device *hwdev, size_t size, void *vaddr, dma_addr_t dma_handle)
 {
-	free_pages((unsigned long) vaddr, get_order(size));
+	if (!(vaddr >= (void *)io_tlb_start
+                    && vaddr < (void *)io_tlb_end))
+		free_pages((unsigned long) vaddr, get_order(size));
+	else
+		/* DMA_TO_DEVICE to avoid memcpy in unmap_single */
+		swiotlb_unmap_single (hwdev, dma_handle, size, DMA_TO_DEVICE);
 }
 
 static void swiotlb_full(struct device *dev, size_t size, int dir, int do_panic)