# Re: \[PATCH v4 03/38\] iommu: add generic helper for mapping sgtable objects

- From: Christoph Hellwig \<hch@lst.de\>
- Date: 2020-05-12 12:18:52 
- List: linux-arm-kernel
- Page: https://ratatoskr.run/linux-arm-kernel/2020/05/5962234
- Thread: https://ratatoskr.run/linux-arm-kernel/2020/05/5962025/t.md

```text
On Tue, May 12, 2020 at 11:00:23AM +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 mapping functions with a wrong number of entries.
> 
> To avoid such issues, lets introduce a common wrapper 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>

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
```