Re: [Xen-devel] [PATCH v8 13/19] swiotlb-xen: use xen_dma_map/unmap_page, xen_dma_sync_single_for_cpu/device

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 23 Oct 2013, Konrad Rzeszutek Wilk wrote:
> 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.

map_page on arm calls the right cache flushes needed to communicate with
the device. Same with unmap_page.
On x86 they are basically nop.
Only map_page and unmap_page know exactly what needs to be done to
map a page for dma, this is why we need to call them here.


> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > ---
> >  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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