AMD
Socket AM3: Chipsets AMD 890FX and 990FX has official IOMMU support
build in in the Chipset itself. Of interesing note, is that albeit there
seems to be other people that got the other 9xx series Chipsets working
with AMD-Vi (On Xen wiki 970 and 990X are included, but not the 980G),
AMD says on a Tech Doc that only the 990FX Chipset got support for it
(Page 9, 1.1):

http://support.amd.com/us/ChipsetMotherboard_TechDocs/48691.pdf

Additionally,
I heared that Bulldozer based PRocessors (Including AMD FX series
Zambezi and Vishera, APUs Trinity and Richland) have another IOMMU built
in. Considering this, you could potentially have two IOMMUs on Socket
AM3+ if you have a Bulldozer based PRocessor with one of the previous
two Chipsets. I have not confirmed this through. So the following
combinations are possible:

K10 based PRocessor on 890FX or 990FX Chipset *MUST WORK*
K10 based PRocessor on 970, 980G or 990X *SHOULD NOT WORK*
Bulldozer based PRocessor on ANY Chipset *SHOULD WORK*
Bulldozer based PRocessor on 890FX or 990FX Chipset *MUST WORK*... just what IOMMU it uses?


AMD
Socket FM1: There should be NO support on this platform. Llano, being
K10 based, doesn't have a build in IOMMU, and the Chipsets doesn't have
it, either.

AMD Socket FM2: As every PRocessor here is Bulldozer
derived, you should have IOMMU support in all them. Besides the newer
A85X, the other Chipsets are the same that on FM1 platform. ASRock
released two beta BIOSes that claims to include IOMMU support on at
least two Motherboard models that includes A55 (FM2A55 Pro) and A75
(FM2A75M-DGS) Chipsets:

http://www.asRock.com/mb/overview.asp?cat=Download&os=Beta&Model=FM2A75M-DGS
http://www.asRock.com/mb/AMD/FM2A55%20Pro/?cat=Beta

So I should suppose that information was correct.