Subject: Re: Using netconsole for debugging suspend/resume

From: Andi Kleen <[email-masked]>
Date: Tue, 13 Jun 2006 06:54:14 +0200

On Tuesday 13 June 2006 06:49, David Miller wrote:
> From: Andi Kleen <[email-masked]>
> Date: Tue, 13 Jun 2006 05:47:49 +0200
> 
> > I've been playing with the idea of writing "early1394" that just
> > turns the DMA controller on as early as possible similar to earlyprintk
> > on the target. Then it would be possible to use it for early
> > debugging too. But so far it's not done yet.
> 
> Does this raw1394 thing with firescope just assume DMA address ==
> physical address? 

Yes.

> How would it work to access all of physical 
> memory properly on IOMMU platforms?

It assumes you don't have an IOMMU - relies on all memory
being accessible by ohci1394. On x86-64 it can't access > 4GB 
also, but that's normally ok because the kernel log buffer
is below that.

I guess if you use 1394 with remote DMA for other protocols (like
video etc.) there must be some way for the subsystem to map
the memory even on IOMMU systems. I admit I haven't dived that
deeply into the 1394 subsystem so I don't know how that works.

-Andi