# Re: \[PATCH v3 02/25\] drm: core: fix common struct sg\_table related issues

- From: Marek Szyprowski \<m.szyprowski@samsung.com\>
- Date: 2020-05-12 09:05:16 
- List: linux-arm-kernel
- Page: https://ratatoskr.run/linux-arm-kernel/2020/05/5962088
- Thread: https://ratatoskr.run/dri-devel/2020/05/5962088/t.md

```text
Hi Christoph,

On 08.05.2020 09:16, Christoph Hellwig wrote:
> On Fri, May 08, 2020 at 09:12:13AM +0200, Marek Szyprowski wrote:
>> Then we would just need one more helper to construct scatterlist, as the
>> above two are read-only don't allow to modify scatterlist:
>>
>> #define for_each_sgtable_sg(sgt, sg, i)                \
>>          for_each_sg(sgt->sgl, sg, sgt->orig_nents, i)
>>
>> With the above 3 helpers we can probably get rid of all instances of
>> sg_table->{nents,orig_nents} from the DRM code. I will prepare patches soon.
> Sounds great, thanks!

It turned out that the 4th helper (for_each_sgtable_dma_sg) was needed 
as some drivers makes use of the larger than the PAGE_SIZE unit for DMA 
mapped pages.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland


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