common: DMA-mapping: add NON-CONSISTENT attribute

DMA_ATTR_NON_CONSISTENT lets the platform to choose to return either
consistent or non-consistent memory as it sees fit.  By using this API,
you are guaranteeing to the platform that you have all the correct and
necessary sync points for this memory in the driver.
Signed-off-by: NMarek Szyprowski <m.szyprowski@samsung.com>
Acked-by: NKyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: NArnd Bergmann <arnd@arndb.de>

Documentation/DMA-attributes.txt

@@ -41,3 +41,11 @@ buffered to improve performance.
 Since it is optional for platforms to implement DMA_ATTR_WRITE_COMBINE,
 those that do not will simply ignore the attribute and exhibit default
 behavior.
+
+DMA_ATTR_NON_CONSISTENT
+-----------------------
+
+DMA_ATTR_NON_CONSISTENT lets the platform to choose to return either
+consistent or non-consistent memory as it sees fit.  By using this API,
+you are guaranteeing to the platform that you have all the correct and
+necessary sync points for this memory in the driver.

include/linux/dma-attrs.h

@@ -14,6 +14,7 @@ enum dma_attr {
 	DMA_ATTR_WRITE_BARRIER,
 	DMA_ATTR_WEAK_ORDERING,
 	DMA_ATTR_WRITE_COMBINE,
+	DMA_ATTR_NON_CONSISTENT,
 	DMA_ATTR_MAX,
 };