IOMMU/AGP troubles on AMD64

From: Sven Köhler
Date: Mon Mar 08 2004 - 15:35:46 EST


i've bought a new Motherboard: Asrock K8S8X (SiS 755 based)

It's running pretty fine, but i can only use 448MB of my 512MB memory.
So here's why:

Checking aperture...
CPU 0: aperture @ e0000000 size 32 MB
Aperture from northbridge cpu 0 too small (32 MB)
AGP bridge at 00:00:00
Aperture from AGP @ e0000000 size 32 MB (APSIZE 38)
Aperture from AGP bridge too small (32 MB)
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 @ 4000000

This is what the kernel tells me when booting.
I already mailed to Asrock that this might be an issue with their BIOS, but the answer was very "untechnical":

We did not test Linux.
If you need Linux driver, please check from SiS Web Site.

The problem is, that i don't know enought to decide, if this is an issue than can be fixed in the Linux-Kernel or if this problem should/must be fixed in the BIOS. There is no IOMMU-Option in the BIOS.


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