Messages in this thread | | | Date | Mon, 9 Jan 2012 09:39:48 +0900 | Subject | Re: [PATCH v3 0/2] ARM: IOMMU: tegra: Add iommu_ops for GART/SMMU driver | From | KyongHo Cho <> |
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On Thu, Jan 5, 2012 at 9:53 PM, Russell King - ARM Linux <linux@arm.linux.org.uk> wrote: > On Thu, Jan 05, 2012 at 09:17:18AM +0200, Hiroshi Doyu wrote: >> Just for DMA mapping test from MPU side, the following one is used. > > This patch is buggy. > >> +static void dmaapi_test_map_page(struct device *dev) >> +{ >> + struct page *page; >> + dma_addr_t dma_addr; >> + void *cpu_addr; >> + >> + page = alloc_page(GFP_KERNEL); >> + BUG_ON(!page); >> + >> + dma_addr = dma_map_page(dev, page, 0, PAGE_SIZE, DMA_TO_DEVICE); >> + BUG_ON(!dma_addr); >> + >> + cpu_addr = kmap(page); >> + BUG_ON(!cpu_addr); >> + memset(cpu_addr, 0xa5, PAGE_SIZE); >> + kunmap(cpu_addr); > > The DMA API works like this: > > - The CPU owns the page or buffer and can access it. > - You map the page or buffer. > - The device owns the page or buffer; the CPU must explicitly access it.
I don't understand what "CPU must __explicitly__ access it" means.
Do you mean that CPU must access the mapped buffer when it __explicitly__ knows that the access does not cause any side effect?
> - You unmap the page or buffer. > - The CPU again owns the page/buffer and can access it. > > Please respect the DMA API rules. > > So. Once dma_map_page() has returned, you must not kmap() or otherwise > access the data contained in that page until after you have unmapped it. > _______________________________________________ > iommu mailing list > iommu@lists.linux-foundation.org > https://lists.linuxfoundation.org/mailman/listinfo/iommu -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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