dma-debug: add comment for failed to check map error

Add comment for failure to check a map error to help driver developers.

Link: http://lkml.kernel.org/r/1484622289-22085-1-git-send-email-miles.chen@mediatek.com
Signed-off-by: Miles Chen <miles.chen@mediatek.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index 8971370bfb16..60c57ec936db 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -1155,6 +1155,11 @@ static void check_unmap(struct dma_debug_entry *ref)
                            dir2name[ref->direction]);
         }
 
+        /*
+         * Drivers should use dma_mapping_error() to check the returned
+         * addresses of dma_map_single() and dma_map_page().
+         * If not, print this warning message. See Documentation/DMA-API.txt.
+         */
         if (entry->map_err_type == MAP_ERR_NOT_CHECKED) {
                 err_printk(ref->dev, entry,
                            "DMA-API: device driver failed to check map error"