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RE: [Xen-devel] allocating AGP aperture memory

  • To: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
  • From: "Langsdorf, Mark" <mark.langsdorf@xxxxxxx>
  • Date: Tue, 18 Oct 2005 17:48:59 -0500
  • Delivery-date: Tue, 18 Oct 2005 22:45:56 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcXUItEVdqWcbj10TmOmktd1+s3AmQADf3OQAAEy7AA=
  • Thread-topic: [Xen-devel] allocating AGP aperture memory

> > I'm still working on getting IOMMU support for Opterons under Xen.
> > 
> > During the boot sequence, Dom0 is finding the aperture
> > through the AGP controller at address 0xe8000000 like it 
> > should.  During AGP controller initialization, though, it 
> > fails to reserve the address space because the necessary 
> > pages are PageReserved in the mem_map.
> Trying to looks a bus (machine) address up in dom0's mem_map
> (pseudo-physical) won't yield anything sensible.

So how do I do this?

> Presumably the driver isn't expecting to find memory behind 
> the aperture? Is it just trying to reserve the bus address 
> range for purposes of ensuring that other PCI devices don't 
> get allocated to it? 
The aperture is an address space that is not supported
by DRAM.  Writes to the aperture get shifted to other
physical addresses through the magic of the GART.  

So no, the driver doesn't expect memory to actually be
there and I'm just trying to reserve the bus address
range to make sure nothing else gets allocated to it.

Normally, the address range would be initially reserved
by the BIOS and the e820 map would reflect that, but
I suppose that isn't happening with Xen.

-Mark Langsdorf
AMD, Inc.

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