From: Andi Kleen <ak@suse.de>
To: Robert Hancock <hancockr@shaw.ca>
Subject: Re: X86_64 + VIA + 4g problems
Date: Mon, 2 Jan 2006 20:53:31 +0100
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On Monday 02 January 2006 20:18, Robert Hancock wrote:
> Andi Kleen wrote:
> > When you not compile in the SKGE network driver does everything else work?
> > skge supports 64bit DMA, so it shouldn't use any IOMMU.
> 
> Are you sure this is skge? 

I grepped for the output in that badly truncated logfile and skge hit.

> Anyway, even if the driver does support  
> 64-bit DMA, I would be surprised if a desktop motherboard had the 
> Ethernet chip connected via a 64-bit PCI bus.

I meant 64bit DMA, aka double address cycle, not a 64bit wide PCI-X bus.
That works on a 32bit PCI bus too. On modern boards it's likely PCI
Express anyways for on board devices.

> 
> This brings up something I've been wondering. It's possible to run most 
> 64-bit capable PCI devices in a 32-bit slot (i.e. with the 64-bit part 
> hanging out of the slot). In this configuration the device will not be 
> able to use 64-bit DMA (unless it supports dual address cycle). However, 
> who is supposed to detect this and know to not try to use DMA addresses 
> above 4GB on that device? 

64bit PCI-X bus has nothing to do with the addressing capability. It
just gives you more bandwidth.

-Andi
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