On Tue, 20 Nov 2007, Andi Kleen wrote:
>
> > This requires propably working 64bit DMA, which is not possible with
> > the SB600 controller.
>
> It should not no. The remapping is done into the GART which is <4GB
> and that is the address the SB600 sees.
Hmm, I just checked the boot logs of the failing 4GB kernel:
BIOS-e820: 0000000100000000 - 0000000120000000 (usable)
...
CPU 0: aperture @ c000000 size 32 MB
Aperture too small (32 MB)
No AGP bridge found
Your BIOS doesn't leave a aperture memory hole
Please enable the IOMMU option in the BIOS setup
This costs you 64 MB of RAM
Mapping aperture over 65536 KB of RAM @ c000000
Memory: 4055984k/4718592k available (2146k kernel code, 136780k reserved, 1273k data, 296k init)
4718592k * 1024 == 0x120000000
So now we have addresses > 4G and I suspect that this is somehow
related to the problem.
When mem=3500M is given on the kernel command line, we do not use this
address space.
Also is the aperture size of 32MB somehow related to this ?
tglx
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