Re: [RFC PATCH] arm: dma-mapping: fallback allocation for cma failure

[Joonsoo Kim <iamjoonsoo.kim@lge.com>]

On Tue, May 20, 2014 at 02:57:47PM +0900, Gioh Kim wrote:
> 
> Thanks for your advise, Michal Nazarewicz.
> 
> Having discuss with Joonsoo, I'm adding fallback allocation after __alloc_from_contiguous().
> The fallback allocation works if CMA kernel options is turned on but CMA size is zero.

Hello, Gioh.

I also mentioned the case where devices have their specific cma_area.
It means that this device needs memory with some contraint.
Although I'm not familiar with DMA infrastructure, I think that
we should handle this case.

How about below patch?

------------>8----------------
diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 6b00be1..4023434 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -379,7 +379,7 @@ static int __init atomic_pool_init(void)
 	unsigned long *bitmap;
 	struct page *page;
 	struct page **pages;
-	void *ptr;
+	void *ptr = NULL;
 	int bitmap_size = BITS_TO_LONGS(nr_pages) * sizeof(long);
 
 	bitmap = kzalloc(bitmap_size, GFP_KERNEL);
@@ -393,7 +393,8 @@ static int __init atomic_pool_init(void)
 	if (IS_ENABLED(CONFIG_DMA_CMA))
 		ptr = __alloc_from_contiguous(NULL, pool->size, prot, &page,
 					      atomic_pool_init);
-	else
+
+	if (!ptr)
 		ptr = __alloc_remap_buffer(NULL, pool->size, gfp, prot, &page,
 					   atomic_pool_init);
 	if (ptr) {
@@ -701,10 +702,22 @@ static void *__dma_alloc(struct device *dev, size_t size, dma_addr_t *handle,
 		addr = __alloc_simple_buffer(dev, size, gfp, &page);
 	else if (!(gfp & __GFP_WAIT))
 		addr = __alloc_from_pool(size, &page);
-	else if (!IS_ENABLED(CONFIG_DMA_CMA))
-		addr = __alloc_remap_buffer(dev, size, gfp, prot, &page, caller);
-	else
-		addr = __alloc_from_contiguous(dev, size, prot, &page, caller);
+	else {
+		if (IS_ENABLED(CONFIG_DMA_CMA)) {
+			addr = __alloc_from_contiguous(dev, size, prot,
+							&page, caller);
+			/*
+			 * Device specific cma_area means that
+			 * this device needs memory with some contraint.
+			 * So, we can't fall through general remap allocation.
+			 */
+			if (!addr && dev && dev->cma_area)
+				return NULL;
+		}
+
+		addr = __alloc_remap_buffer(dev, size, gfp, prot,
+							&page, caller);
+	}
 
 	if (addr)
 		*handle = pfn_to_dma(dev, page_to_pfn(page));

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