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[PATCH v1 01/16] 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() 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@xxxxxxxxxxxx>
---
 include/linux/dma-map-ops.h |  8 +++-
 include/linux/dma-mapping.h | 35 ++++--------------
 kernel/dma/mapping.c        | 73 +++++++++++++++++++++++++++++++++----
 3 files changed, 78 insertions(+), 38 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..daa1e360f0ee 100644
--- a/include/linux/dma-mapping.h
+++ b/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
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 2b06a809d0b9..30f89d244566 100644
--- a/kernel/dma/mapping.c
+++ b/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 +193,74 @@ 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;
 }
+
+/**
+ * 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)
+               ret = 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
+ */
+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;
+       else if (nents < 0)
+               return nents;
+
+       sgt->nents = nents;
+       return 0;
+}
+EXPORT_SYMBOL(dma_map_sgtable);
+
 void dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg,
                                      int nents, enum dma_data_direction dir,
                                      unsigned long attrs)
-- 
2.20.1




 


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