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    FromAndi Kleen <>
    SubjectRe: Using netconsole for debugging suspend/resume
    DateTue, 13 Jun 2006 06:54:14 +0200
    On Tuesday 13 June 2006 06:49, David Miller wrote:
    > From: Andi Kleen <ak@suse.de>
    > 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
    
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