Re: [PATCH] pci: print out DMA mask info

[FUJITA Tomonori]

On Fri, 10 Oct 2008 16:45:08 -0600
Grant Grundler <grundler@xxxxxxxxxxxxxxxx> 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. 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/