That case, device-specific coherent memory allocation, is handled at 
dma_alloc_coherent in arm_dma_alloc.
__dma_alloc handles only general coherent memory allocation.

I'm sorry missing mention about it.


2014-05-20 오후 3:52, Joonsoo Kim 쓴 글:
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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