linux-kernel - Re: [PATCH 2.6.22.y] ieee1394: revert "sbp2: enforce 32bit DMA mapping"

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Message-id: <46B7A22D.4030909@shaw.ca>
Date:	Mon, 06 Aug 2007 16:35:25 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Stefan Richter <stefanr@...6.in-berlin.de>,
	Olaf Hering <olh@...e.de>, linuxppc-dev@...abs.org,
	stable@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2.6.22.y] ieee1394: revert "sbp2: enforce	32bit	DMA	mapping"

Benjamin Herrenschmidt wrote:
> On Mon, 2007-08-06 at 16:25 -0600, Robert Hancock wrote:
>>> Anyway.  For now I will simply go with what 2.6.23-rc has and what
>>> 2.6.21 had:  No dma_set_mask anywhere in the 1394 subsystem.  We can
>>> revisit this whenever an actual need arises.
>> Not sure this is a very good idea. This seems rather likely to fail on
>> x86_64 machines with >4GB of RAM for example.. 
> 
> Would it ? Isn't the default DMA mask for PCI devices set to 32 bits
> anyway ? In which case, swiotlb will take care of the matter.
> 
> Cheers,
> Ben.

Hmm, that's true, yes. Suppose it shouldn't be a problem then.

I would agree, though, that sbp2 isn't really the place for setting 
this, since the DMA mask is presently a property of the device, not of 
the user..

-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@...pamshaw.ca
Home Page: http://www.roberthancock.com/


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