dma-mapping: allow map_sg() ops to return negative error codes

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() defines three error codes that .map_sg implementations
are allowed to return: -EINVAL, -ENOMEM and -EIO. The latter of which
is a generic return for cases that are passing DMA_MAPPING_ERROR
through.

dma_map_sgtable() will convert a zero error return for old map_sg() ops
into a -EIO 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>
Signed-off-by: Christoph Hellwig <hch@lst.de>

include/linux/dma-map-ops.h

@@ -41,8 +41,9 @@ 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. See
+	 * dma_map_sgtable() for a list of appropriate error codes
+	 * and their meanings.
 	 */
 	int (*map_sg)(struct device *dev, struct scatterlist *sg, int nents,
 			enum dma_data_direction dir, unsigned long attrs);

include/linux/dma-mapping.h

@@ -110,6 +110,8 @@ int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents,
 void dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg,
 				      int nents, enum dma_data_direction dir,
 				      unsigned long attrs);
+int dma_map_sgtable(struct device *dev, struct sg_table *sgt,
+		enum dma_data_direction dir, unsigned long attrs);
 dma_addr_t dma_map_resource(struct device *dev, phys_addr_t phys_addr,
 		size_t size, enum dma_data_direction dir, unsigned long attrs);
 void dma_unmap_resource(struct device *dev, dma_addr_t addr, size_t size,
@@ -174,6 +176,11 @@ static inline void dma_unmap_sg_attrs(struct device *dev,
 		unsigned long attrs)
 {
 }
+static inline int dma_map_sgtable(struct device *dev, struct sg_table *sgt,
+		enum dma_data_direction dir, unsigned long attrs)
+{
+	return -EOPNOTSUPP;
+}
 static inline dma_addr_t dma_map_resource(struct device *dev,
 		phys_addr_t phys_addr, size_t size, enum dma_data_direction dir,
 		unsigned long attrs)
@@ -343,34 +350,6 @@ 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_sgtable - Map the given buffer for DMA
- * @dev:	The device for which to perform the DMA operation
- * @sgt:	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 stored in the given sg_table
- * object for the @dir DMA operation by the @dev device. After success the
- * ownership for the buffer is transferred to the DMA domain.  One has to
- * call dma_sync_sgtable_for_cpu() or dma_unmap_sgtable() to move the
- * 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.
- */
-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)
-		return -EINVAL;
-	sgt->nents = nents;
-	return 0;
-}
-
 /**
  * dma_unmap_sgtable - Unmap the given buffer for DMA
  * @dev:	The device for which to perform the DMA operation

kernel/dma/mapping.c

@@ -177,12 +177,8 @@ 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,
-		enum dma_data_direction dir, unsigned long attrs)
+static 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);
 	int ents;
@@ -197,13 +193,83 @@ 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);
+	else if (WARN_ON_ONCE(ents != -EINVAL && ents != -ENOMEM &&
+			      ents != -EIO && ents != 0))
+		return -EIO;
 
 	return ents;
 }
+
+/**
+ * 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).
+ */
+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)
+		return 0;
+	return ret;
+}
 EXPORT_SYMBOL(dma_map_sg_attrs);
 
+/**
+ * dma_map_sgtable - Map the given buffer for DMA
+ * @dev:	The device for which to perform the DMA operation
+ * @sgt:	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 stored in the given sg_table
+ * object for the @dir DMA operation by the @dev device. After success, the
+ * ownership for the buffer is transferred to the DMA domain.  One has to
+ * call dma_sync_sgtable_for_cpu() or dma_unmap_sgtable() to move the
+ * ownership of the buffer back to the CPU domain before touching the
+ * buffer by the CPU.
+ *
+ * Returns 0 on success or a negative error code on error. The following
+ * error codes are supported with the given meaning:
+ *
+ *   -EINVAL - An invalid argument, unaligned access or other error
+ *	       in usage. Will not succeed if retried.
+ *   -ENOMEM - Insufficient resources (like memory or IOVA space) to
+ *	       complete the mapping. Should succeed if retried later.
+ *   -EIO    - Legacy error code with an unknown meaning. eg. this is
+ *	       returned if a lower level call returned DMA_MAPPING_ERROR.
+ */
+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)
+		return -EIO;
+	if (nents < 0)
+		return nents;
+	sgt->nents = nents;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dma_map_sgtable);
+
 void dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg,
 				      int nents, enum dma_data_direction dir,
 				      unsigned long attrs)