[PATCH v3 01/25] dma-mapping: add generic helpers for mapping sgtable objects

Marek Szyprowski m.szyprowski at samsung.com
Tue May 5 08:45:50 UTC 2020

struct sg_table is a common structure used for describing a memory
buffer. 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 pages (nents entry).

It turned out that it was a common mistake to misuse nents and orig_nents
entries, call 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 introduce a common wrappers operating directly
on the struct sg_table objects, which take care of the proper use of
the nents and orig_nents entries.

Signed-off-by: Marek Szyprowski <m.szyprowski at samsung.com>
 include/linux/dma-mapping.h | 32 ++++++++++++++++++++++++++++++++
 include/linux/iommu.h       |  6 ++++++
 2 files changed, 38 insertions(+)

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index b43116a..8364c20d 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -609,6 +609,36 @@ static inline void dma_sync_single_range_for_device(struct device *dev,
 	return dma_sync_single_for_device(dev, addr + offset, size, dir);
+static inline int dma_map_sgtable_attrs(struct device *dev,
+	struct sg_table *sgt, enum dma_data_direction dir, unsigned long attrs)
+	int n = dma_map_sg_attrs(dev, sgt->sgl, sgt->orig_nents, dir, attrs);
+	if (n > 0) {
+		sgt->nents = n;
+		return 0;
+	}
+	return -EINVAL;
+static inline void dma_unmap_sgtable_attrs(struct device *dev,
+	struct sg_table *sgt, enum dma_data_direction dir, unsigned long attrs)
+	dma_unmap_sg_attrs(dev, sgt->sgl, sgt->orig_nents, dir, attrs);
+static inline void dma_sync_sgtable_for_cpu(struct device *dev,
+	struct sg_table *sgt, enum dma_data_direction dir)
+	dma_sync_sg_for_cpu(dev, sgt->sgl, sgt->orig_nents, dir);
+static inline void dma_sync_sgtable_for_device(struct device *dev,
+	struct sg_table *sgt, enum dma_data_direction dir)
+	dma_sync_sg_for_device(dev, sgt->sgl, sgt->orig_nents, dir);
 #define dma_map_single(d, a, s, r) dma_map_single_attrs(d, a, s, r, 0)
 #define dma_unmap_single(d, a, s, r) dma_unmap_single_attrs(d, a, s, r, 0)
 #define dma_map_sg(d, s, n, r) dma_map_sg_attrs(d, s, n, r, 0)
@@ -617,6 +647,8 @@ static inline void dma_sync_single_range_for_device(struct device *dev,
 #define dma_unmap_page(d, a, s, r) dma_unmap_page_attrs(d, a, s, r, 0)
 #define dma_get_sgtable(d, t, v, h, s) dma_get_sgtable_attrs(d, t, v, h, s, 0)
 #define dma_mmap_coherent(d, v, c, h, s) dma_mmap_attrs(d, v, c, h, s, 0)
+#define dma_map_sgtable(d, s, r) dma_map_sgtable_attrs(d, s, r, 0)
+#define dma_unmap_sgtable(d, s, r) dma_unmap_sgtable_attrs(d, s, r, 0)
 extern int dma_common_mmap(struct device *dev, struct vm_area_struct *vma,
 		void *cpu_addr, dma_addr_t dma_addr, size_t size,
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 7ef8b0b..5106b65 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -466,6 +466,12 @@ extern size_t iommu_map_sg_atomic(struct iommu_domain *domain,
 extern void iommu_set_fault_handler(struct iommu_domain *domain,
 			iommu_fault_handler_t handler, void *token);
+static inline size_t iommu_map_sgtable(struct iommu_domain *domain,
+			unsigned long iova, struct sg_table *sgt, int prot)
+	return iommu_map_sg(domain, iova, sgt->sgl, sgt->orig_nents, prot);
 extern void iommu_get_resv_regions(struct device *dev, struct list_head *list);
 extern void iommu_put_resv_regions(struct device *dev, struct list_head *list);
 extern void generic_iommu_put_resv_regions(struct device *dev,

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