[PATCH v2 08/22] dma-mapping: Allow map_sg() ops to return negative error codes

[Logan Gunthorpe <logang@deltatee.com>]

Allow dma_map_sgtable() to pass errors from the map_sg() ops. This
will be required for returning appropriate error codes when mapping
P2PDMA memory.

Introduce __dma_map_sg_attrs() which will return the raw error code
from the map_sg operation (whether it be negative or zero). Then add a
dma_map_sg_attrs() wrapper to convert any negative errors to zero to
satisfy the existing calling convention.

dma_map_sgtable() will convert a zero error return for old map_sg() ops
into a -EINVAL return and return any negative errors as reported.

This allows map_sg implementations to start returning multiple
negative error codes. Legacy map_sg implementations can continue
to return zero until they are all converted.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
 include/linux/dma-map-ops.h |  8 ++++++--
 include/linux/dma-mapping.h | 41 ++++++++++++++++++++++++++++++++-----
 kernel/dma/mapping.c        | 13 +++++-------
 3 files changed, 47 insertions(+), 15 deletions(-)

diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
index 0d53a96a3d64..eaa969be8284 100644
--- a/include/linux/dma-map-ops.h
+++ b/include/linux/dma-map-ops.h
@@ -41,8 +41,12 @@ struct dma_map_ops {
 			size_t size, enum dma_data_direction dir,
 			unsigned long attrs);
 	/*
-	 * map_sg returns 0 on error and a value > 0 on success.
-	 * It should never return a value < 0.
+	 * 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.
 	 */
 	int (*map_sg)(struct device *dev, struct scatterlist *sg, int nents,
 			enum dma_data_direction dir, unsigned long attrs);
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 183e7103a66d..2b0ecf0aa4df 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -105,7 +105,7 @@ dma_addr_t dma_map_page_attrs(struct device *dev, struct page *page,
 		unsigned long attrs);
 void dma_unmap_page_attrs(struct device *dev, dma_addr_t addr, size_t size,
 		enum dma_data_direction dir, unsigned long attrs);
-int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents,
+int __dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents,
 		enum dma_data_direction dir, unsigned long attrs);
 void dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg,
 				      int nents, enum dma_data_direction dir,
@@ -164,7 +164,7 @@ static inline void dma_unmap_page_attrs(struct device *dev, dma_addr_t addr,
 		size_t size, enum dma_data_direction dir, unsigned long attrs)
 {
 }
-static inline int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg,
+static inline int __dma_map_sg_attrs(struct device *dev, struct scatterlist *sg,
 		int nents, enum dma_data_direction dir, unsigned long attrs)
 {
 	return 0;
@@ -343,6 +343,34 @@ static inline void dma_sync_single_range_for_device(struct device *dev,
 	return dma_sync_single_for_device(dev, addr + offset, size, dir);
 }
 
+/**
+ * dma_map_sg_attrs - Map the given buffer for DMA
+ * @dev:	The device for which to perform the DMA operation
+ * @sg:	The sg_table object describing the buffer
+ * @dir:	DMA direction
+ * @attrs:	Optional DMA attributes for the map operation
+ *
+ * Maps a buffer described by a scatterlist passed in the sg argument with
+ * nents segments for the @dir DMA operation by the @dev device.
+ *
+ * Returns the number of mapped entries (which can be less than nents)
+ * on success. Zero is returned for any error.
+ *
+ * dma_unmap_sg_attrs() should be used to unmap the buffer with the
+ * original sg and original nents (not the value returned by this funciton).
+ */
+static inline int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg,
+		int nents, enum dma_data_direction dir, unsigned long attrs)
+{
+	int ret;
+
+	ret = __dma_map_sg_attrs(dev, sg, nents, dir, attrs);
+	if (ret < 0)
+		ret = 0;
+
+	return ret;
+}
+
 /**
  * dma_map_sgtable - Map the given buffer for DMA
  * @dev:	The device for which to perform the DMA operation
@@ -357,16 +385,19 @@ static inline void dma_sync_single_range_for_device(struct device *dev,
  * ownership of the buffer back to the CPU domain before touching the
  * buffer by the CPU.
  *
- * Returns 0 on success or -EINVAL on error during mapping the buffer.
+ * Returns 0 on success or a negative error code on error
  */
 static inline int dma_map_sgtable(struct device *dev, struct sg_table *sgt,
 		enum dma_data_direction dir, unsigned long attrs)
 {
 	int nents;
 
-	nents = dma_map_sg_attrs(dev, sgt->sgl, sgt->orig_nents, dir, attrs);
-	if (nents <= 0)
+	nents = __dma_map_sg_attrs(dev, sgt->sgl, sgt->orig_nents, dir, attrs);
+	if (nents == 0)
 		return -EINVAL;
+	else if (nents < 0)
+		return nents;
+
 	sgt->nents = nents;
 	return 0;
 }
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 2b06a809d0b9..700a2bb7cc9e 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -177,11 +177,7 @@ void dma_unmap_page_attrs(struct device *dev, dma_addr_t addr, size_t size,
 }
 EXPORT_SYMBOL(dma_unmap_page_attrs);
 
-/*
- * dma_maps_sg_attrs returns 0 on error and > 0 on success.
- * It should never return a value < 0.
- */
-int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents,
+int __dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents,
 		enum dma_data_direction dir, unsigned long attrs)
 {
 	const struct dma_map_ops *ops = get_dma_ops(dev);
@@ -197,12 +193,13 @@ int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents,
 		ents = dma_direct_map_sg(dev, sg, nents, dir, attrs);
 	else
 		ents = ops->map_sg(dev, sg, nents, dir, attrs);
-	BUG_ON(ents < 0);
-	debug_dma_map_sg(dev, sg, nents, ents, dir);
+
+	if (ents > 0)
+		debug_dma_map_sg(dev, sg, nents, ents, dir);
 
 	return ents;
 }
-EXPORT_SYMBOL(dma_map_sg_attrs);
+EXPORT_SYMBOL(__dma_map_sg_attrs);
 
 void dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg,
 				      int nents, enum dma_data_direction dir,
-- 
2.20.1