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SubjectRe: [PATCH v3 0/2] ARM: IOMMU: tegra: Add iommu_ops for GART/SMMU driver
On Thu, Jan 05, 2012 at 03:29:30PM +0100, Hiroshi Doyu wrote:
> Ok, the above function order should be as below?
>
> page = alloc_page(GFP_KERNEL);
> cpu_addr = kmap(page);
> memset(cpu_addr, 0xa5, PAGE_SIZE);
> dma_addr = dma_map_page(dev, page, 0, PAGE_SIZE, DMA_TO_DEVICE);
> < expect GPU does something >
> dma_unmap_page(dev, dma_addr, PAGE_SIZE, DMA_TO_DEVICE);
> < CPU can access data here again>
> kunmap(cpu_addr);
> __free_page(page);

That should work, but it's not particularly nice to wrap kmap around
the DMA API.

Bear in mind that alloc_page(GFP_KERNEL) will always give you a lowmem
page. So, you might as well do:

page = alloc_page(GFP_KERNEL);
cpu_addr = page_address(page);
memset()
dma_addr = dma_map_single(dev, cpu_addr, PAGE_SIZE, DMA_TO_DEVICE);
< GPU access >
dma_unmap_single(dev, dma_ddr, PAGE_SIZE, DMA_TO_DEVICE);
< CPU access >
__free_page(page);

and this doesn't raise any issues with kmap vs DMA API.


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