arm64: Support DMA_ATTR_WRITE_COMBINE

DMA_ATTR_WRITE_COMBINE is currently ignored. Set the pgprot
appropriately for non coherent opperations.
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/mm/dma-mapping.c

@@ -30,6 +30,16 @@
 struct dma_map_ops *dma_ops;
 EXPORT_SYMBOL(dma_ops);
 
+static pgprot_t __get_dma_pgprot(struct dma_attrs *attrs, pgprot_t prot,
+				 bool coherent)
+{
+	if (dma_get_attr(DMA_ATTR_WRITE_COMBINE, attrs))
+		return pgprot_writecombine(prot);
+	else if (!coherent)
+		return pgprot_dmacoherent(prot);
+	return prot;
+}
+
 static void *__dma_alloc_coherent(struct device *dev, size_t size,
 				  dma_addr_t *dma_handle, gfp_t flags,
 				  struct dma_attrs *attrs)
@@ -104,7 +114,7 @@ static void *__dma_alloc_noncoherent(struct device *dev, size_t size,
 	for (i = 0; i < (size >> PAGE_SHIFT); i++)
 		map[i] = page + i;
 	coherent_ptr = vmap(map, size >> PAGE_SHIFT, VM_MAP,
-			    pgprot_dmacoherent(pgprot_default));
+			    __get_dma_pgprot(attrs, pgprot_default, false));
 	kfree(map);
 	if (!coherent_ptr)
 		goto no_map;
@@ -250,7 +260,7 @@ static int __swiotlb_mmap_noncoherent(struct device *dev,
 		void *cpu_addr, dma_addr_t dma_addr, size_t size,
 		struct dma_attrs *attrs)
 {
-	vma->vm_page_prot = pgprot_dmacoherent(vma->vm_page_prot);
+	vma->vm_page_prot = __get_dma_pgprot(attrs, vma->vm_page_prot, false);
 	return __dma_common_mmap(dev, vma, cpu_addr, dma_addr, size);
 }