Re: [PATCH 03/11] xen/arm: simplify dma_cache_maint

Stefano Stabellini
2019-08-29T22:43:43Z

On Mon, 26 Aug 2019, Christoph Hellwig wrote:
> Calculate the required operation in the caller, and pass it directly
> instead of recalculating it for each page, and use simple arithmetics
> to get from the physical address to Xen page size aligned chunks.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> arch/arm/xen/mm.c | 62 +++++++++++++++++------------------------------
> 1 file changed, 22 insertions(+), 40 deletions(-)
>
> diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
> index 90574d89d0d4..14210ebdea1a 100644
> --- a/arch/arm/xen/mm.c
> +++ b/arch/arm/xen/mm.c
> @@ -35,64 +35,46 @@ unsigned long xen_get_swiotlb_free_pages(unsigned int order)
> return __get_free_pages(flags, order);
> }
>
> -enum dma_cache_op {
> - DMA_UNMAP,
> - DMA_MAP,
> -};
> static bool hypercall_cflush = false;
>
> -/* functions called by SWIOTLB */
> -
> -static void dma_cache_maint(dma_addr_t handle, unsigned long offset,
> - size_t size, enum dma_data_direction dir, enum dma_cache_op op)
> +/* buffers in highmem or foreign pages cannot cross page boundaries */
> +static void dma_cache_maint(dma_addr_t handle, size_t size, u32 op)
> {
> struct gnttab_cache_flush cflush;
> - unsigned long xen_pfn;
> - size_t left = size;
>
> - xen_pfn = (handle >> XEN_PAGE_SHIFT) + offset / XEN_PAGE_SIZE;
> - offset %= XEN_PAGE_SIZE;
> + cflush.a.dev_bus_addr = handle & XEN_PAGE_MASK;
> + cflush.offset = xen_offset_in_page(handle);
> + cflush.op = op;
>
> do {
> - size_t len = left;
> -
> - /* buffers in highmem or foreign pages cannot cross page
> - * boundaries */
> - if (len + offset > XEN_PAGE_SIZE)
> - len = XEN_PAGE_SIZE - offset;
> -
> - cflush.op = 0;
> - cflush.a.dev_bus_addr = xen_pfn << XEN_PAGE_SHIFT;
> - cflush.offset = offset;
> - cflush.length = len;
> -
> - if (op == DMA_UNMAP && dir != DMA_TO_DEVICE)
> - cflush.op = GNTTAB_CACHE_INVAL;
> - if (op == DMA_MAP) {
> - if (dir == DMA_FROM_DEVICE)
> - cflush.op = GNTTAB_CACHE_INVAL;
> - else
> - cflush.op = GNTTAB_CACHE_CLEAN;
> - }
> - if (cflush.op)
> - HYPERVISOR_grant_table_op(GNTTABOP_cache_flush, &cflush, 1);
> + if (size + cflush.offset > XEN_PAGE_SIZE)
> + cflush.length = XEN_PAGE_SIZE - cflush.offset;
> + else
> + cflush.length = size;

isn't it missing a:

cflush.a.dev_bus_addr = handle & XEN_PAGE_MASK;

here?

> + HYPERVISOR_grant_table_op(GNTTABOP_cache_flush, &cflush, 1);
> +
> + handle += cflush.length;
> + size -= cflush.length;
>
> - offset = 0;
> - xen_pfn++;
> - left -= len;
> - } while (left);
> + cflush.offset = 0;
> + } while (size);
> }
>
> static void __xen_dma_page_dev_to_cpu(struct device *hwdev, dma_addr_t handle,
> size_t size, enum dma_data_direction dir)
> {
> - dma_cache_maint(handle & PAGE_MASK, handle & ~PAGE_MASK, size, dir, DMA_UNMAP);
> + if (dir != DMA_TO_DEVICE)
> + dma_cache_maint(handle, size, GNTTAB_CACHE_INVAL);
> }
>
> static void __xen_dma_page_cpu_to_dev(struct device *hwdev, dma_addr_t handle,
> size_t size, enum dma_data_direction dir)
> {
> - dma_cache_maint(handle & PAGE_MASK, handle & ~PAGE_MASK, size, dir, DMA_MAP);
> + if (dir == DMA_FROM_DEVICE)
> + dma_cache_maint(handle, size, GNTTAB_CACHE_INVAL);
> + else
> + dma_cache_maint(handle, size, GNTTAB_CACHE_CLEAN);
> }
>
> void __xen_dma_map_page(struct device *hwdev, struct page *page,
> --
> 2.20.1