Re: [Xen-devel] [PATCH 3/4] swiotlb-xen: simplify the DMA sync method implementations

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 11 Apr 2019, Christoph Hellwig wrote:
> Get rid of the grand multiplexer and implement the sync_single_for_cpu
> and sync_single_for_device methods directly, and then loop over them
> for the scatterlist based variants.
> 
> Note that this also loses a few comments related to highlevel DMA API
> concepts, which have nothing to do with the swiotlb-xen implementation
> details.
> 
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

> ---
>  drivers/xen/swiotlb-xen.c | 84 +++++++++++++--------------------------
>  1 file changed, 28 insertions(+), 56 deletions(-)
> 
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index 97a55c225593..9a951504dc12 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -455,48 +455,28 @@ static void xen_swiotlb_unmap_page(struct device 
> *hwdev, dma_addr_t dev_addr,
>       xen_unmap_single(hwdev, dev_addr, size, dir, attrs);
>  }
>  
> -/*
> - * Make physical memory consistent for a single streaming mode DMA 
> translation
> - * after a transfer.
> - *
> - * If you perform a xen_swiotlb_map_page() but wish to interrogate the buffer
> - * using the cpu, yet do not wish to teardown the dma mapping, you must
> - * call this function before doing so.  At the next point you give the dma
> - * address back to the card, you must first perform a
> - * xen_swiotlb_dma_sync_for_device, and then the device again owns the buffer
> - */
>  static void
> -xen_swiotlb_sync_single(struct device *hwdev, dma_addr_t dev_addr,
> -                     size_t size, enum dma_data_direction dir,
> -                     enum dma_sync_target target)
> +xen_swiotlb_sync_single_for_cpu(struct device *dev, dma_addr_t dma_addr,
> +             size_t size, enum dma_data_direction dir)
>  {
> -     phys_addr_t paddr = xen_bus_to_phys(dev_addr);
> +     phys_addr_t paddr = xen_bus_to_phys(dma_addr);
>  
> -     BUG_ON(dir == DMA_NONE);
> -
> -     if (target == SYNC_FOR_CPU)
> -             xen_dma_sync_single_for_cpu(hwdev, dev_addr, size, dir);
> +     xen_dma_sync_single_for_cpu(dev, dma_addr, size, dir);
>  
> -     /* NOTE: We use dev_addr here, not paddr! */
> -     if (is_xen_swiotlb_buffer(dev_addr))
> -             swiotlb_tbl_sync_single(hwdev, paddr, size, dir, target);
> -
> -     if (target == SYNC_FOR_DEVICE)
> -             xen_dma_sync_single_for_device(hwdev, dev_addr, size, dir);
> +     if (is_xen_swiotlb_buffer(dma_addr))
> +             swiotlb_tbl_sync_single(dev, paddr, size, dir, SYNC_FOR_CPU);
>  }
>  
> -void
> -xen_swiotlb_sync_single_for_cpu(struct device *hwdev, dma_addr_t dev_addr,
> -                             size_t size, enum dma_data_direction dir)
> +static void
> +xen_swiotlb_sync_single_for_device(struct device *dev, dma_addr_t dma_addr,
> +             size_t size, enum dma_data_direction dir)
>  {
> -     xen_swiotlb_sync_single(hwdev, dev_addr, size, dir, SYNC_FOR_CPU);
> -}
> +     phys_addr_t paddr = xen_bus_to_phys(dma_addr);
>  
> -void
> -xen_swiotlb_sync_single_for_device(struct device *hwdev, dma_addr_t dev_addr,
> -                                size_t size, enum dma_data_direction dir)
> -{
> -     xen_swiotlb_sync_single(hwdev, dev_addr, size, dir, SYNC_FOR_DEVICE);
> +     if (is_xen_swiotlb_buffer(dma_addr))
> +             swiotlb_tbl_sync_single(dev, paddr, size, dir, SYNC_FOR_DEVICE);
> +
> +     xen_dma_sync_single_for_device(dev, dma_addr, size, dir);
>  }
>  
>  /*
> @@ -541,38 +521,30 @@ xen_swiotlb_map_sg(struct device *dev, struct 
> scatterlist *sgl, int nelems,
>       return 0;
>  }
>  
> -/*
> - * Make physical memory consistent for a set of streaming mode DMA 
> translations
> - * after a transfer.
> - *
> - * The same as swiotlb_sync_single_* but for a scatter-gather list, same 
> rules
> - * and usage.
> - */
>  static void
> -xen_swiotlb_sync_sg(struct device *hwdev, struct scatterlist *sgl,
> -                 int nelems, enum dma_data_direction dir,
> -                 enum dma_sync_target target)
> +xen_swiotlb_sync_sg_for_cpu(struct device *dev, struct scatterlist *sgl,
> +                         int nelems, enum dma_data_direction dir)
>  {
>       struct scatterlist *sg;
>       int i;
>  
> -     for_each_sg(sgl, sg, nelems, i)
> -             xen_swiotlb_sync_single(hwdev, sg->dma_address,
> -                                     sg_dma_len(sg), dir, target);
> -}
> -
> -static void
> -xen_swiotlb_sync_sg_for_cpu(struct device *hwdev, struct scatterlist *sg,
> -                         int nelems, enum dma_data_direction dir)
> -{
> -     xen_swiotlb_sync_sg(hwdev, sg, nelems, dir, SYNC_FOR_CPU);
> +     for_each_sg(sgl, sg, nelems, i) {
> +             xen_swiotlb_sync_single_for_cpu(dev, sg->dma_address,
> +                             sg->length, dir);
> +     }
>  }
>  
>  static void
> -xen_swiotlb_sync_sg_for_device(struct device *hwdev, struct scatterlist *sg,
> +xen_swiotlb_sync_sg_for_device(struct device *dev, struct scatterlist *sgl,
>                              int nelems, enum dma_data_direction dir)
>  {
> -     xen_swiotlb_sync_sg(hwdev, sg, nelems, dir, SYNC_FOR_DEVICE);
> +     struct scatterlist *sg;
> +     int i;
> +
> +     for_each_sg(sgl, sg, nelems, i) {
> +             xen_swiotlb_sync_single_for_device(dev, sg->dma_address,
> +                             sg->length, dir);
> +     }
>  }

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