In SPARC land, at least on SunOS and Solaris, it was very convenient for
debugging to interrupt the OS with Stop-A and use OFW to inspect the
system state. That was especially handy for live crash analysis. Dumps
are useful as far as they go, but they often fail to capture detailed
I/O device state.
I was hoping to do that on x86 too. So far we (OLPC) haven't
implemented a sysrq hook to enter OFW, but I haven't given up hope yet.
It doesn't cost much to leave OFW around, but once you decide to eject
it, you can't easily get it back.
Apple made the early decision to eject OFW and just keep a device tree
table. That decision was probably due to several factors, including the
rather lame state of Apple's first OFW implementation and the complexity
of their OS startup process at the time (which included "trampolining"
to a 68000 emulator to run their legacy code). Once they went down that
path, the die was cast, and the PowerPC community got used to the "OFW
ends up as just a table" idea.
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