Re: [PATCH v2 2/2] arm64: Add support for DMA_ATTR_FORCE_CONTIGUOUS to IOMMU

[Laurent Pinchart]

Hi Geert,

Thank you for the patch.

On Friday 27 Jan 2017 16:34:19 Geert Uytterhoeven wrote:
> Add support for allocation physically contiguous DMA buffers on arm64
> systems with an IOMMU, by dispatching DMA buffer allocations with the
> DMA_ATTR_FORCE_CONTIGUOUS attribute to the appropriate IOMMU DMA
> helpers.
> 
> Note that as this uses the CMA allocator, setting this 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 <geert+renesas@xxxxxxxxx>
> ---
> v2:
>   - New, handle dispatching in the arch (arm64) code, as requested by
>     Robin Murphy.
> ---
>  arch/arm64/mm/dma-mapping.c | 51 +++++++++++++++++++++++++++++-------------
>  1 file changed, 37 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
> index 1d7d5d2881db7c19..325803e0ba79ef26 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 +601,35 @@ 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 = iommu_dma_alloc_contiguous(dev, iosize, ioprot, 
handle);
> +		if (!page)
> +			return NULL;
> +
> +		if (!coherent)
> +			__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_free_contiguous(dev, page, iosize, handle);
> +	} 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;
>  }
> @@ -626,6 +642,8 @@ 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:

s/one of 3/one of 4/

Apart from that,

Acked-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>

> +	 * - A remapped array of pages from iommu_dma_alloc_contiguous()
> +	 *   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 +655,11 @@ 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));
> +
> +		iommu_dma_free_contiguous(dev, page, iosize, &handle);
> +		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);

-- 
Regards,

Laurent Pinchart