dma_alloc_coherent: clean it up

This thing was rather stupidly coded.  Rework it all prior to making
changes.

Also, rename local variable `page': kernel readers expect something called
`page' to have type `struct page *'.

Cc: Guennadi Liakhovetski <lg@denx.de>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Dmitry Baryshkov <dbaryshkov@gmail.com>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/dma-coherent.c

@@ -109,34 +109,38 @@ EXPORT_SYMBOL(dma_mark_declared_memory_occupied);
 int dma_alloc_from_coherent(struct device *dev, ssize_t size,
 				       dma_addr_t *dma_handle, void **ret)
 {
-	struct dma_coherent_mem *mem = dev ? dev->dma_mem : NULL;
+	struct dma_coherent_mem *mem;
 	int order = get_order(size);
+	int pageno;
 
-	if (mem) {
-		int page = bitmap_find_free_region(mem->bitmap, mem->size,
-						     order);
-		if (page >= 0) {
-			/*
-			 * Memory was found in the per-device arena.
-			 */
-			*dma_handle = mem->device_base + (page << PAGE_SHIFT);
-			*ret = mem->virt_base + (page << PAGE_SHIFT);
-			memset(*ret, 0, size);
-		} else if (mem->flags & DMA_MEMORY_EXCLUSIVE) {
-			/*
-			 * The per-device arena is exhausted and we are not
-			 * permitted to fall back to generic memory.
-			 */
-			*ret = NULL;
-		} else {
-			/*
-			 * The per-device arena is exhausted and we are
-			 * permitted to fall back to generic memory.
-			 */
-			 return 0;
-		}
+	if (!dev)
+		return 0;
+	mem = dev->dma_mem;
+	if (!mem)
+		return 0;
+
+	pageno = bitmap_find_free_region(mem->bitmap, mem->size, order);
+	if (pageno >= 0) {
+		/*
+		 * Memory was found in the per-device arena.
+		 */
+		*dma_handle = mem->device_base + (pageno << PAGE_SHIFT);
+		*ret = mem->virt_base + (pageno << PAGE_SHIFT);
+		memset(*ret, 0, size);
+	} else if (mem->flags & DMA_MEMORY_EXCLUSIVE) {
+		/*
+		 * The per-device arena is exhausted and we are not
+		 * permitted to fall back to generic memory.
+		 */
+		*ret = NULL;
+	} else {
+		/*
+		 * The per-device arena is exhausted and we are
+		 * permitted to fall back to generic memory.
+		 */
+		 return 0;
 	}
-	return (mem != NULL);
+	return 1;
 }
 EXPORT_SYMBOL(dma_alloc_from_coherent);