Ide emulation issue is not on qemu list yet. From what I see here it is not really a driver implementation fault because driver callback gets bogus pointer. Probably this is caused by some clash with low memory location where device i/o space is mapped.
Pardon my ignorance, but are you saying that Qemu is throwing a bogus pointer back to OpenBIOS, or that there's something wrong with OpenBIOS that's requesting the wrong memory location? So is it worth opening a thread on the qemu-devel list, or is everyone who needs to work the problem already on this list?
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