On Tue, May 12, 2020 at 11:00:21AM +0200, 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 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 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
For more information, see '[PATCH v4 00/38] DRM: fix struct sg_table nents vs. orig_nents misuse' thread: https://lore.kernel.org/dri-devel/20200512085710.14688-1-m.szyprowski@samsun...
include/linux/dma-mapping.h | 79 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 79 insertions(+)
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h index b43116a..88f01cc 100644 --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -609,6 +609,85 @@ 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 the DMA operations
- @dev: The device to perform a 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 n = dma_map_sg_attrs(dev, sgt->sgl, sgt->orig_nents, dir, attrs);
- if (n > 0) {
sgt->nents = n;return 0;- }
- return -EINVAL;
Nit: code tend to be a tad easier to read if the the exceptional condition is inside the branch block, so:
if (n <= 0) return -EINVAL; sgt->nents = n; return 0;
Otherwise this looks good to me:
Reviewed-by: Christoph Hellwig hch@lst.de