Hi Marek,
On 05/05/2020 10:45, Marek Szyprowski wrote:
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 function.
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@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)
Please document these new inline functions!
The core reason IMHO why so many drivers do this wrong is that the struct sg_table documentation is very poor. In particular w.r.t. how the nents and orig_nents fields should be used.
It confused me, and clearly I am not alone in that.
So while this is a very nice improvement, it doesn't address the core issue, i.e. the documentation.
Especially some examples on how to use these new functions would be welcome.
Regards,
Hans
+{
- 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,