[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,

Eugene




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