Messages in this thread |  | | Date | Fri, 10 Oct 2008 16:45:08 -0600 | From | Grant Grundler <> | Subject | Re: [PATCH] pci: print out DMA mask info |
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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.
> 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".
> Some drivers don't set up coherent_dma_mask.
They probably should. Current default is 32-bits for PCI devices.
> Theoretically, we need to fix this but it doesn't cause any > problem. That's why nobody cares about it, I guess.
Agreed - for the "supported" configurations, it works.
hth, grant
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