Re: [1/3] Add 4GB DMA32 zone

[Alan Cox]

> One argument was still if the zone should be 4GB or 2GB. The main
> motivation for 2GB would be an unnamed not so unpopular hardware
> raid controller (mostly found in older machines from a particular four letter
> company) who has a strange 2GB restriction in firmware. But 

Adaptec AACRAID is one offender

> that one works ok with swiotlb/IOMMU anyways, so it doesn't really

Old aacraid actually cannot use IOMMU. It isn't alone in that
limitation. Most hardware that has a 30/31bit limit can't go via the
IOMMU because IOMMU space appears on the bus above 2GB so is itself
invisible to the hardware.

Other devices with similar limits include the broadcomm b44


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