Hi Geert,
On 31/01/17 11:12, Geert Uytterhoeven wrote:
> Add support for allocating physically contiguous DMA buffers on arm64
> systems with an IOMMU. This can be useful when two or more devices
> with different memory requirements are involved in buffer sharing.
>
> Note that as this uses the CMA allocator, setting the
> DMA_ATTR_FORCE_CONTIGUOUS attribute has a runtime-dependency on
> CONFIG_DMA_CMA, just like on arm32.
>
> For arm64 systems using swiotlb, no changes are needed to support the
> allocation of physically contiguous DMA buffers:
> - swiotlb always uses physically contiguous buffers (up to
> IO_TLB_SEGSIZE = 128 pages),
> - arm64's __dma_alloc_coherent() already calls
> dma_alloc_from_contiguous() when CMA is available.
>
> Signed-off-by: Geert Uytterhoeven <[email protected]>
> Acked-by: Laurent Pinchart <[email protected]>
> ---
> v3:
> - Add Acked-by,
> - Update comment to "one of _4_ things",
> - Call dma_alloc_from_contiguous() and iommu_dma_map_page() directly,
> as suggested by Robin Murphy,
>
> v2:
> - New, handle dispatching in the arch (arm64) code, as requested by
> Robin Murphy.
> ---
> arch/arm64/mm/dma-mapping.c | 63
> ++++++++++++++++++++++++++++++++++-----------
> 1 file changed, 48 insertions(+), 15 deletions(-)
>
> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
> index 1d7d5d2881db7c19..b314256fcee028ce 100644
> --- a/arch/arm64/mm/dma-mapping.c
> +++ b/arch/arm64/mm/dma-mapping.c
> @@ -577,20 +577,7 @@ static void *__iommu_alloc_attrs(struct device *dev,
> size_t size,
> */
> gfp |= __GFP_ZERO;
>
> - if (gfpflags_allow_blocking(gfp)) {
> - struct page **pages;
> - pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL, coherent);
> -
> - pages = iommu_dma_alloc(dev, iosize, gfp, attrs, ioprot,
> - handle, flush_page);
> - if (!pages)
> - return NULL;
> -
> - addr = dma_common_pages_remap(pages, size, VM_USERMAP, prot,
> - __builtin_return_address(0));
> - if (!addr)
> - iommu_dma_free(dev, pages, iosize, handle);
> - } else {
> + if (!gfpflags_allow_blocking(gfp)) {
> struct page *page;
> /*
> * In atomic context we can't remap anything, so we'll only
> @@ -614,6 +601,45 @@ static void *__iommu_alloc_attrs(struct device *dev,
> size_t size,
> __free_from_pool(addr, size);
> addr = NULL;
> }
> + } else if (attrs & DMA_ATTR_FORCE_CONTIGUOUS) {
> + pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL, coherent);
> + struct page *page;
> +
> + page = dma_alloc_from_contiguous(dev, size >> PAGE_SHIFT,
> + get_order(size));
> + if (!page)
> + return NULL;
> +
> + *handle = iommu_dma_map_page(dev, page, 0, iosize, ioprot);
> + if (iommu_dma_mapping_error(dev, *handle)) {
> + dma_release_from_contiguous(dev, page,
> + size >> PAGE_SHIFT);
> + return NULL;
> + }
> + if (!coherent)
I think we might be able to return early if coherent here, as the
non-IOMMU __dma_alloc() does. We still need a (cacheable) remap in the
normal coherent case to make whatever pages iommu_dma_alloc() scrapes
together appear contiguous, but that obviously isn't a concern here.
However, I'm not entirely confident that that wouldn't break (or at
least further complicate) the already-horrible "what the hell is this?"
logic in __iommu_free_attrs() below, so I'm inclined to leave it as-is.
> + __dma_flush_area(page_to_virt(page), iosize);
> +
> + addr = dma_common_contiguous_remap(page, size, VM_USERMAP,
> + prot,
> + __builtin_return_address(0));
> + if (!addr) {
> + iommu_dma_unmap_page(dev, *handle, iosize, 0, attrs);
> + dma_release_from_contiguous(dev, page,
> + size >> PAGE_SHIFT);
> + }
> + } else {
> + pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL, coherent);
> + struct page **pages;
> +
> + pages = iommu_dma_alloc(dev, iosize, gfp, attrs, ioprot,
> + handle, flush_page);
> + if (!pages)
> + return NULL;
> +
> + addr = dma_common_pages_remap(pages, size, VM_USERMAP, prot,
> + __builtin_return_address(0));
> + if (!addr)
> + iommu_dma_free(dev, pages, iosize, handle);
> }
> return addr;
> }
> @@ -625,7 +651,8 @@ static void __iommu_free_attrs(struct device *dev, size_t
> size, void *cpu_addr,
>
> size = PAGE_ALIGN(size);
> /*
> - * @cpu_addr will be one of 3 things depending on how it was allocated:
> + * @cpu_addr will be one of 4 things depending on how it was allocated:
> + * - A remapped array of pages for contiguous allocations.
> * - A remapped array of pages from iommu_dma_alloc(), for all
> * non-atomic allocations.
> * - A non-cacheable alias from the atomic pool, for atomic
> @@ -637,6 +664,12 @@ static void __iommu_free_attrs(struct device *dev,
> size_t size, void *cpu_addr,
> if (__in_atomic_pool(cpu_addr, size)) {
> iommu_dma_unmap_page(dev, handle, iosize, 0, 0);
> __free_from_pool(cpu_addr, size);
> + } else if (attrs & DMA_ATTR_FORCE_CONTIGUOUS) {
> + struct page *page = phys_to_page(dma_to_phys(dev, handle));
handle is the IOVA returned by the original iommu_dma_map_page() call,
so I can't see this working very well. I was about to naively suggest
virt_to_page(cpu_addr), except of course cpu_addr isn't going to be a
linear map address :(
I think that works out to another argument in favour of not trying to
skip the remap when coherent, since that would mean we can consistently
rely on vmalloc_to_page(cpu_addr) here, and everything *should* be OK
(crosses fingers...)
Robin.
> +
> + iommu_dma_unmap_page(dev, handle, iosize, 0, attrs);
> + dma_release_from_contiguous(dev, page, size >> PAGE_SHIFT);
> + dma_common_free_remap(cpu_addr, size, VM_USERMAP);
> } else if (is_vmalloc_addr(cpu_addr)){
> struct vm_struct *area = find_vm_area(cpu_addr);
>
>
