Hi,
Doing it the other way around is tricky for initialization order reasons, especially for coreboot. pmbase and mmconf xbar (those are looked up by the qemu acpi table generator) locations are (a) compile time constants and (b) programmed very early at boot time.
Ahh - I vaguely recall discussing this before.
However, I don't think it makes sense for SeaBIOS to have a compile time definition on where to place the mappings. Can't it be pulled from fwcfg?
Current smm code requires pmbase being a compile time constant. IIRC there was a experimental patch changing that last time we discussed this, but it wasn't merged.
Once we have that we can make pmbase depend on fw_cfg, either indirectly (if qemu provides acpi tables it is new enough to handle pmbase being mapped at a non-traditional location), or by qemu suggesting a location in a (to be created) fw_cfg file.
cheers, Gerd