linux-kernel - Re: [PATCH v8 13/19] swiotlb-xen: use xen_dma_map/unmap_page, xen_dma_sync_single_for

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Message-ID: <20131023140927.GD27771@phenom.dumpdata.com>
Date:	Wed, 23 Oct 2013 10:09:27 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	xen-devel@...ts.xensource.com, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, Ian.Campbell@...rix.com
Subject: Re: [PATCH v8 13/19] swiotlb-xen: use xen_dma_map/unmap_page,
 xen_dma_sync_single_for_cpu/device

On Thu, Oct 17, 2013 at 06:43:28PM +0100, Stefano Stabellini wrote:
> Call xen_dma_map_page, xen_dma_unmap_page, xen_dma_sync_single_for_cpu,
> xen_dma_sync_single_for_device from swiotlb-xen to ensure cpu/device
> coherency of the pages used for DMA, including the ones belonging to the
> swiotlb buffer.

You lost me.

Isn't it the driver's responsibility to do this?

Looking at what 'xen_dma_map_page()' does for x86 it looks to add an extra
call - page_to_phys - and we ignore it here.

> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
> ---
>  drivers/xen/swiotlb-xen.c |   39 +++++++++++++++++++++++++++++++--------
>  1 files changed, 31 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index 189b8db..4221cb5 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -378,8 +378,13 @@ dma_addr_t xen_swiotlb_map_page(struct device *dev, struct page *page,
>  	 * buffering it.
>  	 */
>  	if (dma_capable(dev, dev_addr, size) &&
> -	    !range_straddles_page_boundary(phys, size) && !swiotlb_force)
> +	    !range_straddles_page_boundary(phys, size) && !swiotlb_force) {
> +		/* 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(dev, page, offset, size, dir, attrs);
>  		return dev_addr;
> +	}
>  
>  	/*
>  	 * Oh well, have to allocate and map a bounce buffer.
> @@ -388,6 +393,8 @@ dma_addr_t xen_swiotlb_map_page(struct device *dev, struct page *page,
>  	if (map == SWIOTLB_MAP_ERROR)
>  		return DMA_ERROR_CODE;
>  
> +	xen_dma_map_page(dev, pfn_to_page(map >> PAGE_SHIFT),
> +					map & ~PAGE_MASK, size, dir, attrs);
>  	dev_addr = xen_phys_to_bus(map);
>  
>  	/*
> @@ -410,12 +417,15 @@ EXPORT_SYMBOL_GPL(xen_swiotlb_map_page);
>   * whatever the device wrote there.
>   */
>  static void xen_unmap_single(struct device *hwdev, dma_addr_t dev_addr,
> -			     size_t size, enum dma_data_direction dir)
> +			     size_t size, enum dma_data_direction dir,
> +				 struct dma_attrs *attrs)
>  {
>  	phys_addr_t paddr = xen_bus_to_phys(dev_addr);
>  
>  	BUG_ON(dir == DMA_NONE);
>  
> +	xen_dma_unmap_page(hwdev, paddr, size, dir, attrs);
> +
>  	/* NOTE: We use dev_addr here, not paddr! */
>  	if (is_xen_swiotlb_buffer(dev_addr)) {
>  		swiotlb_tbl_unmap_single(hwdev, paddr, size, dir);
> @@ -438,7 +448,7 @@ void xen_swiotlb_unmap_page(struct device *hwdev, dma_addr_t dev_addr,
>  			    size_t size, enum dma_data_direction dir,
>  			    struct dma_attrs *attrs)
>  {
> -	xen_unmap_single(hwdev, dev_addr, size, dir);
> +	xen_unmap_single(hwdev, dev_addr, size, dir, attrs);
>  }
>  EXPORT_SYMBOL_GPL(xen_swiotlb_unmap_page);
>  
> @@ -461,11 +471,15 @@ xen_swiotlb_sync_single(struct device *hwdev, dma_addr_t dev_addr,
>  
>  	BUG_ON(dir == DMA_NONE);
>  
> +	if (target == SYNC_FOR_CPU)
> +		xen_dma_sync_single_for_cpu(hwdev, paddr, size, dir);
> +
>  	/* NOTE: We use dev_addr here, not paddr! */
> -	if (is_xen_swiotlb_buffer(dev_addr)) {
> +	if (is_xen_swiotlb_buffer(dev_addr))
>  		swiotlb_tbl_sync_single(hwdev, paddr, size, dir, target);
> -		return;
> -	}
> +
> +	if (target == SYNC_FOR_DEVICE)
> +		xen_dma_sync_single_for_cpu(hwdev, paddr, size, dir);
>  
>  	if (dir != DMA_FROM_DEVICE)
>  		return;
> @@ -536,8 +550,17 @@ xen_swiotlb_map_sg_attrs(struct device *hwdev, struct scatterlist *sgl,
>  				return DMA_ERROR_CODE;
>  			}
>  			sg->dma_address = xen_phys_to_bus(map);
> -		} else
> +		} 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),
> +						paddr & ~PAGE_MASK,
> +						sg->length,
> +						dir,
> +						attrs);
>  			sg->dma_address = dev_addr;
> +		}
>  		sg_dma_len(sg) = sg->length;
>  	}
>  	return nelems;
> @@ -559,7 +582,7 @@ xen_swiotlb_unmap_sg_attrs(struct device *hwdev, struct scatterlist *sgl,
>  	BUG_ON(dir == DMA_NONE);
>  
>  	for_each_sg(sgl, sg, nelems, i)
> -		xen_unmap_single(hwdev, sg->dma_address, sg_dma_len(sg), dir);
> +		xen_unmap_single(hwdev, sg->dma_address, sg_dma_len(sg), dir, attrs);
>  
>  }
>  EXPORT_SYMBOL_GPL(xen_swiotlb_unmap_sg_attrs);
> -- 
> 1.7.2.5
> 
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