arc: Implement arch-specific dma_map_ops.mmap (a79a8121) · Commits · 戴 / test

We used to use generic implementation of dma_map_ops.mmap which is dma_common_mmap() but that only worked for simpler cached mappings when vaddr = paddr. If a driver requests uncached DMA buffer kernel maps it to virtual address so that MMU gets involved and page uncached status takes into account. In that case usage of dma_common_mmap() lead to mapping of vaddr to vaddr for user-space which is obviously wrong. For more detals please refer to verbose explanation here [1]. So here we implement our own version of mmap() which always deals with dma_addr and maps underlying memory to user-space properly (note that DMA buffer mapped to user-space is always uncached because there's no way to properly manage cache from user-space). [1] https://lkml.org/lkml/2016/10/26/973 Reviewed-by:

Catalin Marinas <catalin.marinas@arm.com> Cc: Marek Szyprowski <m.szyprowski@samsung.com> Cc: <stable@vger.kernel.org> #4.5+ Signed-off-by:

Alexey Brodkin <abrodkin@synopsys.com> Signed-off-by:

Vineet Gupta <vgupta@synopsys.com>

arch/arc/mm/dma.c

+26 −0

Original line number	Diff line number	Diff line
		@@ -105,6 +105,31 @@ static void arc_dma_free(struct device dev, size_t size, void vaddr,
		__free_pages(page, get_order(size));
		}

		static int arc_dma_mmap(struct device dev, struct vm_area_struct vma,
		void *cpu_addr, dma_addr_t dma_addr, size_t size,
		unsigned long attrs)
		{
		unsigned long user_count = vma_pages(vma);
		unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
		unsigned long pfn = __phys_to_pfn(plat_dma_to_phys(dev, dma_addr));
		unsigned long off = vma->vm_pgoff;
		int ret = -ENXIO;

		vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);

		if (dma_mmap_from_coherent(dev, vma, cpu_addr, size, &ret))
		return ret;

		if (off < count && user_count <= (count - off)) {
		ret = remap_pfn_range(vma, vma->vm_start,
		pfn + off,
		user_count << PAGE_SHIFT,
		vma->vm_page_prot);
		}

		return ret;
		}

		/*
		* streaming DMA Mapping API...
		* CPU accesses page via normal paddr, thus needs to explicitly made
		@@ -193,6 +218,7 @@ static int arc_dma_supported(struct device *dev, u64 dma_mask)
		struct dma_map_ops arc_dma_ops = {
		.alloc = arc_dma_alloc,
		.free = arc_dma_free,
		.mmap = arc_dma_mmap,
		.map_page = arc_dma_map_page,
		.map_sg = arc_dma_map_sg,
		.sync_single_for_device = arc_dma_sync_single_for_device,

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