Re: [Xen-devel] [PATCH 2/4] swiotlb-xen: use ->map_page to implement ->map_sg

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 11 Apr 2019, Christoph Hellwig wrote:
> We can simply loop over the segments and map them, removing lots of
> duplicate code.

Right, the only difference is the additional dma_capable check which is
good to have.

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
>  drivers/xen/swiotlb-xen.c | 68 ++++++---------------------------------
>  1 file changed, 10 insertions(+), 58 deletions(-)
> 
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index d4bc3aabd44d..97a55c225593 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -517,24 +517,8 @@ xen_swiotlb_unmap_sg(struct device *hwdev, struct 
> scatterlist *sgl, int nelems,
>  
>  }
>  
> -/*
> - * Map a set of buffers described by scatterlist in streaming mode for DMA.
> - * This is the scatter-gather version of the above xen_swiotlb_map_page
> - * interface.  Here the scatter gather list elements are each tagged with the
> - * appropriate dma address and length.  They are obtained via
> - * sg_dma_{address,length}(SG).
> - *
> - * NOTE: An implementation may be able to use a smaller number of
> - *       DMA address/length pairs than there are SG table elements.
> - *       (for example via virtual mapping capabilities)
> - *       The routine returns the number of addr/length pairs actually
> - *       used, at most nents.
> - *
> - * Device ownership issues as mentioned above for xen_swiotlb_map_page are 
> the
> - * same here.
> - */
>  static int
> -xen_swiotlb_map_sg(struct device *hwdev, struct scatterlist *sgl, int nelems,
> +xen_swiotlb_map_sg(struct device *dev, struct scatterlist *sgl, int nelems,
>               enum dma_data_direction dir, unsigned long attrs)
>  {
>       struct scatterlist *sg;
> @@ -543,50 +527,18 @@ xen_swiotlb_map_sg(struct device *hwdev, struct 
> scatterlist *sgl, int nelems,
>       BUG_ON(dir == DMA_NONE);
>  
>       for_each_sg(sgl, sg, nelems, i) {
> -             phys_addr_t paddr = sg_phys(sg);
> -             dma_addr_t dev_addr = xen_phys_to_bus(paddr);
> -
> -             if (swiotlb_force == SWIOTLB_FORCE ||
> -                 xen_arch_need_swiotlb(hwdev, paddr, dev_addr) ||
> -                 !dma_capable(hwdev, dev_addr, sg->length) ||
> -                 range_straddles_page_boundary(paddr, sg->length)) {
> -                     phys_addr_t map = swiotlb_tbl_map_single(hwdev,
> -                                                              start_dma_addr,
> -                                                              sg_phys(sg),
> -                                                              sg->length,
> -                                                              dir, attrs);
> -                     if (map == DMA_MAPPING_ERROR) {
> -                             dev_warn(hwdev, "swiotlb buffer is full\n");
> -                             /* Don't panic here, we expect map_sg users
> -                                to do proper error handling. */
> -                             attrs |= DMA_ATTR_SKIP_CPU_SYNC;
> -                             xen_swiotlb_unmap_sg(hwdev, sgl, i, dir, attrs);
> -                             sg_dma_len(sgl) = 0;
> -                             return 0;
> -                     }
> -                     dev_addr = xen_phys_to_bus(map);
> -                     xen_dma_map_page(hwdev, pfn_to_page(map >> PAGE_SHIFT),
> -                                             dev_addr,
> -                                             map & ~PAGE_MASK,
> -                                             sg->length,
> -                                             dir,
> -                                             attrs);
> -                     sg->dma_address = dev_addr;
> -             } else {
> -                     /* we are not interested in the dma_addr returned by
> -                      * xen_dma_map_page, only in the potential cache 
> flushes executed
> -                      * by the function. */
> -                     xen_dma_map_page(hwdev, pfn_to_page(paddr >> 
> PAGE_SHIFT),
> -                                             dev_addr,
> -                                             paddr & ~PAGE_MASK,
> -                                             sg->length,
> -                                             dir,
> -                                             attrs);
> -                     sg->dma_address = dev_addr;
> -             }
> +             sg->dma_address = xen_swiotlb_map_page(dev, sg_page(sg),
> +                             sg->offset, sg->length, dir, attrs);
> +             if (sg->dma_address == DMA_MAPPING_ERROR)
> +                     goto out_unmap;
>               sg_dma_len(sg) = sg->length;
>       }
> +
>       return nelems;
> +out_unmap:
> +     xen_swiotlb_unmap_sg(dev, sgl, i, dir, attrs | DMA_ATTR_SKIP_CPU_SYNC);
> +     sg_dma_len(sgl) = 0;
> +     return 0;
>  }
>  
>  /*
> -- 
> 2.20.1
> 

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