On Tue, 11 Nov 2008 14:32:46 -0600 (CST) Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx> wrote: > On Tue, 11 Nov 2008, FUJITA Tomonori wrote: > > > Is it because it does some kinda address translation > > (provider->dma_map_consistent) later? The zone flag is meaningless if > > you do sorta address translation (e.g. hardware IOMMU like VT-d). > > Yes it can do address translation. Therefore a < 4G address can show up at > any 64 bit address. So no need for a special DMA zone. The same is true > for more x86_64 platforms that have an IOMMU. Yes, with address translation hardware such as IOMMU, the zone is meaningless. The IOMMU drivers ignore the zone flag (e.g. intel_alloc_coherent). But the GFP_DMA in IA64's platform_dma_alloc_coherent() is still necessary for swiotlb with devices that don't have DMA_64BIT_MASK coherent_dma_mask. They need a < 4G address. This is exactly what x86 and x86_64 do, dma_alloc_coherent in arch/x86/include/asm/dma-mapping.h. It sets GFP_DMA and GFP_DMA32 for swiotlb and pci-nommu.c when necessary. -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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