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Subject[PATCH v10 25/30] dmabuf: fix common struct sg_table related issues
The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg() function
returns the number of the created entries in the DMA address space.
However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and
dma_unmap_sg must be called with the original number of the entries
passed to the dma_map_sg().

struct sg_table is a common structure used for describing a non-contiguous
memory buffer, used commonly in the DRM and graphics subsystems. It
consists of a scatterlist with memory pages and DMA addresses (sgl entry),
as well as the number of scatterlist entries: CPU pages (orig_nents entry)
and DMA mapped pages (nents entry).

It turned out that it was a common mistake to misuse nents and orig_nents
entries, calling DMA-mapping functions with a wrong number of entries or
ignoring the number of mapped entries returned by the dma_map_sg()

To avoid such issues, lets use a common dma-mapping wrappers operating
directly on the struct sg_table objects and use scatterlist page
iterators where possible. This, almost always, hides references to the
nents and orig_nents entries, making the code robust, easier to follow
and copy/paste safe.

Signed-off-by: Marek Szyprowski <>
Acked-by: Gerd Hoffmann <>
drivers/dma-buf/heaps/heap-helpers.c | 13 ++++++-------
drivers/dma-buf/udmabuf.c | 7 +++----
2 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/drivers/dma-buf/heaps/heap-helpers.c b/drivers/dma-buf/heaps/heap-helpers.c
index 9f964ca3f59c..d0696cf937af 100644
--- a/drivers/dma-buf/heaps/heap-helpers.c
+++ b/drivers/dma-buf/heaps/heap-helpers.c
@@ -140,13 +140,12 @@ struct sg_table *dma_heap_map_dma_buf(struct dma_buf_attachment *attachment,
enum dma_data_direction direction)
struct dma_heaps_attachment *a = attachment->priv;
- struct sg_table *table;
- table = &a->table;
+ struct sg_table *table = &a->table;
+ int ret;

- if (!dma_map_sg(attachment->dev, table->sgl, table->nents,
- direction))
- table = ERR_PTR(-ENOMEM);
+ ret = dma_map_sgtable(attachment->dev, table, direction, 0);
+ if (ret)
+ table = ERR_PTR(ret);
return table;

@@ -154,7 +153,7 @@ static void dma_heap_unmap_dma_buf(struct dma_buf_attachment *attachment,
struct sg_table *table,
enum dma_data_direction direction)
- dma_unmap_sg(attachment->dev, table->sgl, table->nents, direction);
+ dma_unmap_sgtable(attachment->dev, table, direction, 0);

static vm_fault_t dma_heap_vm_fault(struct vm_fault *vmf)
diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index acb26c627d27..89e293bd9252 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -63,10 +63,9 @@ static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf,
if (ret < 0)
goto err;
- if (!dma_map_sg(dev, sg->sgl, sg->nents, direction)) {
- ret = -EINVAL;
+ ret = dma_map_sgtable(dev, sg, direction, 0);
+ if (ret < 0)
goto err;
- }
return sg;

@@ -78,7 +77,7 @@ static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf,
static void put_sg_table(struct device *dev, struct sg_table *sg,
enum dma_data_direction direction)
- dma_unmap_sg(dev, sg->sgl, sg->nents, direction);
+ dma_unmap_sgtable(dev, sg, direction, 0);
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