On Tue, Jun 09, 2015 at 12:27:10PM -0400, Dan Williams wrote:
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index 7e7583ddd607..9f6ff6671f01 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -1502,7 +1502,7 @@ static int __map_sg_chunk(struct device *dev, struct
> scatterlist *sg,
> return -ENOMEM;
>
> for (count = 0, s = sg; count < (size >> PAGE_SHIFT); s = sg_next(s)) {
> - phys_addr_t phys = page_to_phys(sg_page(s));
> + phys_addr_t phys = sg_phys(s) - s->offset;
So sg_phys() turns out to be 'page_to_phys(sg_page(s)) + s->offset',
which makes the above statement to:
page_to_phys(sg_page(s)) + s->offset - s->offset;
The compiler will probably optimize that away, but it still doesn't look
like an improvement.
> unsigned int len = PAGE_ALIGN(s->offset + s->length);
>
> if (!is_coherent &&
> diff --git a/arch/microblaze/kernel/dma.c b/arch/microblaze/kernel/dma.c
> index ed7ba8a11822..dcb3c594d626 100644
> --- a/arch/microblaze/kernel/dma.c
> +++ b/arch/microblaze/kernel/dma.c
> @@ -61,7 +61,7 @@ static int dma_direct_map_sg(struct device *dev, struct
> scatterlist *sgl,
> /* FIXME this part of code is untested */
> for_each_sg(sgl, sg, nents, i) {
> sg->dma_address = sg_phys(sg);
> - __dma_sync(page_to_phys(sg_page(sg)) + sg->offset,
> + __dma_sync(sg_phys(sg),
> sg->length, direction);
Here the replacement makes sense, but weird indendation. Could all be
moved to one line, I guess.
> }
>
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 68d43beccb7e..9b9ada71e0d3 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -1998,7 +1998,7 @@ static int __domain_mapping(struct dmar_domain *domain,
> unsigned long iov_pfn,
> sg_res = aligned_nrpages(sg->offset, sg->length);
> sg->dma_address = ((dma_addr_t)iov_pfn <<
> VTD_PAGE_SHIFT) + sg->offset;
> sg->dma_length = sg->length;
> - pteval = page_to_phys(sg_page(sg)) | prot;
> + pteval = (sg_phys(sg) - sg->offset) | prot;
Here it doesn't make sense too. In general, please remove the cases
where you have to subtract sg->offset after the conversion.
Joerg
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