Subject: Re: [TG3]: Add DMA address workaround
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Michael Chan <mchan@broadcom.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       "David S. Miller" <davem@davemloft.net>,
       Anton Blanchard <anton@samba.org>, Paul Mackerras <paulus@samba.org>
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Date: Wed, 08 Mar 2006 11:28:04 +1100
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On Tue, 2006-03-07 at 14:18 -0800, Michael Chan wrote:

> So how does powerpc handle 32-bit PCI devices that don't support dual
> address cycles? Such devices will set the dma_mask to 32-bit. Shouldn't
> 40-bit be handled in a similar way?

I've double checked that our current DMA code always stays below 32
bits. I was more wondering about some not-yet there stuff but it looks
like we are safe on that side too.

One thing i've been looking into doing with the iommu code is to make it
capable of respecting the DMA mask precisely (by constraining the
allocator to any arbitrary mask, not just 32 vs. 64 bits) to make it
more useful for bcm44xx and 43xx... but that's a different story.

Ben.


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