[discuss] Out of IOMMU space

Eugene BT eugene.devilliers at btinternet.com
Mon Sep 12 18:53:12 CEST 2005

Andi Kleen wrote:
>On Friday 09 September 2005 14:35, Eugene BT wrote:
>>The board only has a PCI-e graphics card, so I should be able to use
>>iommu=noagp with a larger apperture.
>The code should detect that case (no real AGP bridge in the system) 
>automatically and default to iommu=noagp. You should see
>PCI-DMA: Disabling AGP.
>early in your boot log.
Interesting. This is the relevant extract from my boot log:

<4>Checking aperture...
<4>CPU 0: aperture @ 0 size 2048 MB
<4>No AGP bridge found
<4>Your BIOS doesn't leave a aperture memory hole
<4>Please enable the IOMMU option in the BIOS setup
<4>This costs you 64 MB of RAM
<4>Mapping aperture over 65536 KB of RAM @ 4000000

The thing is I have enabled IOMMU in the BIOS, so I am not quite clear 
why the kernel displays the "please enable the IOMMU" request.

> So only truly increasing the aperture with 
>iommu=memaper=3 (=128MB) or larger will help, unless the BIOS
>setup has an option to increase the IOMMU.
Nope, the BIOS allows me to switch IOMMU on or off and has the option to 
set the size of what it calls a "memory hole". Not a lot of information 
available in the manuals to what exactly this refers to.
For the time being I have set "iommu=memaper=3" in the boot options and 
am waiting to see what impact this has.

Thanks again,


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