On Saturday 26 January 2008, Olof Johansson wrote:

quoted

So instead of having an IOMMU window that we use to temporarily map things
in and out of DMA'able space, at boot we create a 1:1 mapping for all of
memory. This obviously only works for devices that can do 64-bit DMA.

I don't get it. Why not disable the iommu instead?

When you disable the iommu, the 32-bit devices stop working because
they can no longer access all of main memory.

The 1:1 mapping is in addition to the DMA window used for those devices,
not in place of it.

	Arnd <><