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SubjectRe: [PATCH 08/10] swiotlb-xen: introduce phys_to_dma/dma_to_phys translations
From
Date
Hi,

On 21/05/2020 00:45, Stefano Stabellini wrote:
> From: Stefano Stabellini <stefano.stabellini@xilinx.com>
>
> Call dma_to_phys in is_xen_swiotlb_buffer.
> Call phys_to_dma in xen_phys_to_bus.
> Call dma_to_phys in xen_bus_to_phys.
>
> Everything is taken care of by these changes except for
> xen_swiotlb_alloc_coherent and xen_swiotlb_free_coherent, which need a
> few explicit phys_to_dma/dma_to_phys calls.

The commit message explains what the code is doing but doesn't explain
why this is needed.

>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>
> ---
> drivers/xen/swiotlb-xen.c | 20 ++++++++++++--------
> 1 file changed, 12 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index c50448fd9b75..d011c4c7aa72 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -64,14 +64,16 @@ static inline dma_addr_t xen_phys_to_bus(struct device *dev, phys_addr_t paddr)
>
> dma |= paddr & ~XEN_PAGE_MASK;
>
> - return dma;
> + return phys_to_dma(dev, dma);
> }
>
> -static inline phys_addr_t xen_bus_to_phys(struct device *dev, dma_addr_t baddr)
> +static inline phys_addr_t xen_bus_to_phys(struct device *dev,
> + dma_addr_t dma_addr)
> {
> + phys_addr_t baddr = dma_to_phys(dev, dma_addr);
> unsigned long xen_pfn = bfn_to_pfn(XEN_PFN_DOWN(baddr));
> - dma_addr_t dma = (dma_addr_t)xen_pfn << XEN_PAGE_SHIFT;
> - phys_addr_t paddr = dma;
> + phys_addr_t paddr = (xen_pfn << XEN_PAGE_SHIFT) |
> + (baddr & ~XEN_PAGE_MASK);
>
> paddr |= baddr & ~XEN_PAGE_MASK;
>
> @@ -99,7 +101,7 @@ static inline int range_straddles_page_boundary(phys_addr_t p, size_t size)
>
> static int is_xen_swiotlb_buffer(struct device *dev, dma_addr_t dma_addr)
> {
> - unsigned long bfn = XEN_PFN_DOWN(dma_addr);
> + unsigned long bfn = XEN_PFN_DOWN(dma_to_phys(dev, dma_addr));
> unsigned long xen_pfn = bfn_to_local_pfn(bfn);
> phys_addr_t paddr = XEN_PFN_PHYS(xen_pfn);
>
> @@ -304,11 +306,11 @@ xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
> if (hwdev && hwdev->coherent_dma_mask)
> dma_mask = hwdev->coherent_dma_mask;
>
> - /* At this point dma_handle is the physical address, next we are
> + /* At this point dma_handle is the dma address, next we are
> * going to set it to the machine address.
> * Do not use virt_to_phys(ret) because on ARM it doesn't correspond
> * to *dma_handle. */
> - phys = *dma_handle;
> + phys = dma_to_phys(hwdev, *dma_handle);
> dev_addr = xen_phys_to_bus(hwdev, phys);
> if (((dev_addr + size - 1 <= dma_mask)) &&
> !range_straddles_page_boundary(phys, size))
> @@ -319,6 +321,7 @@ xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
> xen_free_coherent_pages(hwdev, size, ret, (dma_addr_t)phys, attrs);
> return NULL;
> }
> + *dma_handle = phys_to_dma(hwdev, *dma_handle);
> SetPageXenRemapped(virt_to_page(ret));
> }
> memset(ret, 0, size);
> @@ -351,7 +354,8 @@ xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
> TestClearPageXenRemapped(pg))
> xen_destroy_contiguous_region(phys, order);
>
> - xen_free_coherent_pages(hwdev, size, vaddr, (dma_addr_t)phys, attrs);
> + xen_free_coherent_pages(hwdev, size, vaddr, phys_to_dma(hwdev, phys),
> + attrs);
> }
>
> /*
>

Cheers,

--
Julien Grall

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