dma-direct: add support for CMA allocation

Try the CMA allocator for coherent allocations if supported.

Roughly modelled after the x86 code.
Signed-off-by: Christoph Hellwig <hch@lst.de>

lib/dma-direct.c

@@ -7,6 +7,7 @@
 #include <linux/mm.h>
 #include <linux/dma-direct.h>
 #include <linux/scatterlist.h>
+#include <linux/dma-contiguous.h>
 #include <linux/pfn.h>
 
 #define DIRECT_MAPPING_ERROR		0
@@ -29,19 +30,30 @@ check_addr(struct device *dev, dma_addr_t dma_addr, size_t size,
 static void *dma_direct_alloc(struct device *dev, size_t size,
 		dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs)
 {
-	void *ret;
+	unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
+	int page_order = get_order(size);
+	struct page *page = NULL;
 
-	ret = (void *)__get_free_pages(gfp, get_order(size));
-	if (ret)
-		*dma_handle = phys_to_dma(dev, virt_to_phys(ret));
+	/* CMA can be used only in the context which permits sleeping */
+	if (gfpflags_allow_blocking(gfp))
+		page = dma_alloc_from_contiguous(dev, count, page_order, gfp);
+	if (!page)
+		page = alloc_pages(gfp, page_order);
+	if (!page)
+		return NULL;
 
-	return ret;
+	*dma_handle = phys_to_dma(dev, page_to_phys(page));
+	memset(page_address(page), 0, size);
+	return page_address(page);
 }
 
 static void dma_direct_free(struct device *dev, size_t size, void *cpu_addr,
 		dma_addr_t dma_addr, unsigned long attrs)
 {
-	free_pages((unsigned long)cpu_addr, get_order(size));
+	unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
+
+	if (!dma_release_from_contiguous(dev, virt_to_page(cpu_addr), count))
+		free_pages((unsigned long)cpu_addr, get_order(size));
 }
 
 static dma_addr_t dma_direct_map_page(struct device *dev, struct page *page,