Hi Christoph,
On 12.05.2020 14:18, Christoph Hellwig wrote:
On Tue, May 12, 2020 at 11:00:21AM +0200, Marek Szyprowski wrote:
quoted
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@samsung.com/T/ (local)
---
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;
Indeed this version looks much better. I will resend it in a few minutes.
Otherwise this looks good to me:
Reviewed-by: Christoph Hellwig <hch@lst.de>
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel