[PATCH v2 01/21] dma-mapping: Allow map_sg() ops to return negative error codes

From: Logan Gunthorpe (logang@xxxxxxxxxxxx)
Date: Fri Jul 23 2021 - 13:50:23 EST


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@xxxxxxxxxxxx>
---
include/linux/dma-map-ops.h | 5 ++-
include/linux/dma-mapping.h | 35 +++------------
kernel/dma/mapping.c | 85 +++++++++++++++++++++++++++++++++----
3 files changed, 87 insertions(+), 38 deletions(-)

diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
index 0d53a96a3d64..2f842498c448 100644
--- a/include/linux/dma-map-ops.h
+++ b/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);
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..b8dc8b1cb402 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 +193,86 @@ 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. 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;
+ else if (nents < 0) {
+ if (WARN_ON_ONCE(nents != -EINVAL && nents != -ENOMEM &&
+ nents != -EIO))
+ return -EIO;
+ 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)
--
2.20.1