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

[FUJITA Tomonori]

On Thu, 09 Oct 2008 16:05:57 -0700
Yinghai Lu <yinghai@xxxxxxxxxx> wrote:

> Grant Grundler wrote:
> > On Thu, Oct 09, 2008 at 02:51:32PM -0700, Yinghai Lu wrote:
> >> On Thu, Oct 9, 2008 at 2:35 PM, Matthew Wilcox <matthew@xxxxxx> wrote:
> >>> Why's that interesting to the sysadmin of the machine?  To the driver
> >>> writer, certainly.  But what's the use of it to the people using the
> >>> machine?
> > ...
> >> make linux kernel act like black box as other os?
> > 
> > I don't understand your reply.
> > If someone thinks linux is a black box, printing this message won't help them.
> > 
> could find out easily why some driver doesn't set dma mask correctly.
> like why 
> 	qlogic qla2xxx only set consistent to 64bit,
> 	emulex lpfc not set consistent to 64bit

IIRC, except for one SGI architecture, coherent_dma_mask is
meaningless, dma_mask is always equal to coherent_dma_mask. Lots of
IOMMU implementations ignore coherent_dma_mask and use dma_mask for
alloc_coherent(). Some drivers doesn't set up coherent_dma_mask.

Theoretically, we need to fix this but it doesn't cause any
problem. That's why nobody cares about it, I guess.
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