Yeah, right please go ahead. But I wonder whether any BIOS was actually crazy enough to map mmio region above 4G on 32bit machine.
This is a *hardware* mapping on some non-x86 platforms (like PPC 44x or MIPS Alchemy). The arch/ppc/ and arch/mips/ kernels have special hooks called from ioremap() which help create an illusion that the PCI memory space on such platforms (not only it) is mapped below 4 GB; arch/powerpc/ kernel doesn't do this anymore -- hence this newly encountered issue.