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Commit a79a8121 authored by Alexey Brodkin's avatar Alexey Brodkin Committed by Vineet Gupta
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arc: Implement arch-specific dma_map_ops.mmap 

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: default avatarCatalin Marinas <catalin.marinas@arm.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: <stable@vger.kernel.org>  #4.5+
Signed-off-by: default avatarAlexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: default avatarVineet Gupta <vgupta@synopsys.com>
parent 8f6d9eb2

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,