include/dma-mapping: Clarify output of dma_map_sg

Although dma_map_sg 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.

Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index c3007cb4bfa6..ac07ff090919 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -34,6 +34,10 @@ struct dma_map_ops {
         void (*unmap_page)(struct device *dev, dma_addr_t dma_handle,
                            size_t size, enum dma_data_direction dir,
                            struct dma_attrs *attrs);
+        /*
+         * map_sg returns 0 on error and a value > 0 on success.
+         * It should never return a value < 0.
+         */
         int (*map_sg)(struct device *dev, struct scatterlist *sg,
                       int nents, enum dma_data_direction dir,
                       struct dma_attrs *attrs);