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SubjectRe: [PATCH 06/21] dma-iommu: use for_each_sg in iommu_dma_alloc
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On 27/03/2019 08:04, Christoph Hellwig wrote:
> arch_dma_prep_coherent can handle physically contiguous ranges larger
> than PAGE_SIZE just fine, which means we don't need a page-based
> iterator.

Heh, I got several minutes into writing a "but highmem..." reply before
finding csky's arch_dma_prep_coherent() implementation. And of course
that's why it specifically takes a page instead of any addresses. In
hindsight I now have no idea why I didn't just write the flush_page()
logic to work that way in the first place...

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> drivers/iommu/dma-iommu.c | 14 +++++---------
> 1 file changed, 5 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 77d704c8f565..f915cb7c46e6 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -577,15 +577,11 @@ struct page **iommu_dma_alloc(struct device *dev, size_t size, gfp_t gfp,
> goto out_free_iova;
>
> if (!(prot & IOMMU_CACHE)) {
> - struct sg_mapping_iter miter;
> - /*
> - * The CPU-centric flushing implied by SG_MITER_TO_SG isn't
> - * sufficient here, so skip it by using the "wrong" direction.
> - */
> - sg_miter_start(&miter, sgt.sgl, sgt.orig_nents, SG_MITER_FROM_SG);
> - while (sg_miter_next(&miter))
> - arch_dma_prep_coherent(miter.page, PAGE_SIZE);
> - sg_miter_stop(&miter);
> + struct scatterlist *sg;
> + int i;
> +
> + for_each_sg(sgt.sgl, sg, sgt.orig_nents, i)
> + arch_dma_prep_coherent(sg_page(sg), sg->length);
> }
>
> if (iommu_map_sg(domain, iova, sgt.sgl, sgt.orig_nents, prot)
>

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