[PATCH 1/2] asm/dma-mapping-common: Clarify output of dma_map_sg_attrs

From: Ricardo Ribalda Delgado
Date: Wed Feb 11 2015 - 07:53:24 EST

Although dma_map_sg_attrs returns 0 on error and it cannot return a
value < 0, the function returns a signed integer.

Most of the time, this function is used with a scatterlist structure.
This structure uses an unsigned integer for the number of memory.

A dma developer that has not read in detail DMA-API.txt, can wrongly
return a value < 0 on error.

The comment will help the driver developer, and the WARN_ON the dma

Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@xxxxxxxxx>
include/asm-generic/dma-mapping-common.h | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/include/asm-generic/dma-mapping-common.h b/include/asm-generic/dma-mapping-common.h
index 3378dcf..940d5ec 100644
--- a/include/asm-generic/dma-mapping-common.h
+++ b/include/asm-generic/dma-mapping-common.h
@@ -39,6 +39,10 @@ static inline void dma_unmap_single_attrs(struct device *dev, dma_addr_t addr,
debug_dma_unmap_page(dev, addr, size, dir, true);

+ * dma_maps_sg_attrs returns 0 on error and > 0 on success.
+ * It should never return a value < 0.
+ */
static inline int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg,
int nents, enum dma_data_direction dir,
struct dma_attrs *attrs)
@@ -51,6 +55,7 @@ static inline int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg,
kmemcheck_mark_initialized(sg_virt(s), s->length);
ents = ops->map_sg(dev, sg, nents, dir, attrs);
+ BUG_ON(ents < 0);
debug_dma_map_sg(dev, sg, nents, ents, dir);

return ents;

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