[PATCH v1 16/16] dma-mapping: Disallow .map_sg operations from returning zero on error

[Logan Gunthorpe <logang@xxxxxxxxxxxx>]

Now that all the .map_sg operations have been converted to returning
proper error codes, drop the code to handle a zero return value,
add a warning if a zero is returned and update the comment for the
map_sg operation.

Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
---
 include/linux/dma-map-ops.h | 8 +++-----
 kernel/dma/mapping.c        | 6 +++---
 2 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
index eaa969be8284..f299bc1e317b 100644
--- a/include/linux/dma-map-ops.h
+++ b/include/linux/dma-map-ops.h
@@ -42,11 +42,9 @@ struct dma_map_ops {
                        unsigned long attrs);
        /*
         * map_sg should return a negative error code on error.
-        * dma_map_sgtable() will return the error code returned and convert
-        * a zero return (for legacy implementations) into -EINVAL.
-        *
-        * dma_map_sg() will always return zero on any negative or zero
-        * return to satisfy its own calling convention.
+        * dma_map_sgtable() will return the error code returned by the
+        * operation and dma_map_sg() will always convert any error to zero
+        * to satisfy its own calling convention.
         */
        int (*map_sg)(struct device *dev, struct scatterlist *sg, int nents,
                        enum dma_data_direction dir, unsigned long attrs);
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 30f89d244566..978a6a16aaf7 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -194,6 +194,8 @@ static int __dma_map_sg_attrs(struct device *dev, struct 
scatterlist *sg,
        else
                ents = ops->map_sg(dev, sg, nents, dir, attrs);
 
+       WARN_ON_ONCE(ents == 0);
+
        if (ents > 0)
                debug_dma_map_sg(dev, sg, nents, ents, dir);
 
@@ -251,9 +253,7 @@ int dma_map_sgtable(struct device *dev, struct sg_table 
*sgt,
        int nents;
 
        nents = __dma_map_sg_attrs(dev, sgt->sgl, sgt->orig_nents, dir, attrs);
-       if (nents == 0)
-               return -EINVAL;
-       else if (nents < 0)
+       if (nents < 0)
                return nents;
 
        sgt->nents = nents;
-- 
2.20.1