Messages in this thread | | | Date | Tue, 14 Oct 2008 15:50:02 +0900 | Subject | Re: [PATCH] pci: print out DMA mask info | From | FUJITA Tomonori <> |
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On Fri, 10 Oct 2008 16:45:08 -0600 Grant Grundler <grundler@parisc-linux.org> wrote:
> On Fri, Oct 10, 2008 at 11:40:56AM +0900, FUJITA Tomonori wrote: > > IIRC, except for one SGI architecture, coherent_dma_mask is > > meaningless, dma_mask is always equal to coherent_dma_mask. > > Not correct. Several PCI-X devices can only do 32-bit DMA to control > data but can do 64-bit DMA for payload data. I don't have the list off > the top of my head but that is the origin of coherent DMA mask.
Thanks. I misunderstood coherent_dma_mask. I needed to read several old mails (posted in 2002 and 2003) in ia64 mailing list.
> > Lots of > > IOMMU implementations ignore coherent_dma_mask and use dma_mask for > > alloc_coherent(). > > That sounds like a bug. And I don't think it's "lots".
Maybe it's not "lots" but seems that only IA64 and x86 non-hardware IOMMU code (pci-nommu.c and GART) use coherent_dma_mask for alloc_coherent.
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