linux-kernel - Re: [PATCH] pci: print out DMA mask info

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Date:	Thu, 9 Oct 2008 21:56:33 -0700
From:	"Yinghai Lu" <yinghai@...nel.org>
To:	"FUJITA Tomonori" <fujita.tomonori@....ntt.co.jp>
Cc:	grundler@...isc-linux.org, matthew@....cx,
	jbarnes@...tuousgeek.org, mingo@...e.hu, tglx@...utronix.de,
	hpa@...or.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH] pci: print out DMA mask info

On Thu, Oct 9, 2008 at 7:40 PM, FUJITA Tomonori
<fujita.tomonori@....ntt.co.jp> wrote:
> On Thu, 09 Oct 2008 16:05:57 -0700
> Yinghai Lu <yinghai@...nel.org> 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@....cx> 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.

ehci_hcd 0000:00:02.1: using 31bit consistent DMA mask
==> ck804 ehci, is using 31bit for consistent dma mask, at still use
32 bit for dma mask.

qlogic qla2xxx  and emulex lpfc dma mask and consistent_dma_mask is different...
could have some story for them

at least gart iommu is honoring the consistent dma mask.
by calling dma_alloc_coherent_mask(dev, flag)

if device could use 64 bit coherent dma mask, that is driver problem...
print it out could put them in focus.

YH
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