Freebios2 recovery progress... pci64 mem optimization
YhLu at tyan.com
Thu Oct 21 21:33:01 CEST 2004
You are right
PCI-DMA: Disabling IOMMU.
PCI-DMA: Disabling AGP.
PCI-DMA: aperture base @ 8000000 size 65536 KB
PCI-DMA: Reserving 64MB of IOMMU area in the AGP aperture
From: ebiederman at lnxi.com [mailto:ebiederman at lnxi.com]
Sent: Thursday, October 21, 2004 7:40 PM
Subject: Re: Freebios2 recovery progress... pci64 mem optimization
YhLu <YhLu at tyan.com> writes:
> Iommu is only needed when system installed memory > 4G?
IOMMU's have 2 uses.
1) let devices with small DMA ranges reach all of memory
(pci devices that don't implement DAC can only talk to the first 4G)
2) Isolation. Allowing the OS to controll which memory may be touched
by I/O devices.
The current Opteron IOMMU does not appear to be general enough to
perform isolation so it is only needed when you have more than 4GB of
So there may be some point in disabling it on systems with 4GB.
Plus the linux kernel seems to be able to properly allocate the iommu
if it needs it.
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