add is_buffer_dma_capable helper function

is_buffer_dma_capable helper function is to see if a memory region is
DMA-capable or not. The arugments are the dma_mask (or
coherent_dma_mask) of a device and the address and size of a memory
region.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Acked-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/dma-mapping.h

@@ -48,6 +48,11 @@ static inline int is_device_dma_capable(struct device *dev)
 	return dev->dma_mask != NULL && *dev->dma_mask != DMA_MASK_NONE;
 }
 
+static inline int is_buffer_dma_capable(u64 mask, dma_addr_t addr, size_t size)
+{
+	return addr + size <= mask;
+}
+
 #ifdef CONFIG_HAS_DMA
 #include <asm/dma-mapping.h>
 #else