That register is in the config space BAR region, so it should be ok to
write 0xffffffff to it and read it back to size the register. However,
it's after writing the 0xffffffff to it and trying to read it back that
the machine hangs. I didn't see any accesses to the command register to
disable decoding (at least not via the mmconfig methods), so maybe that's
broken during MCFG based probing?
Jesse
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