and is also a good reason why exposing this information via a common interface (fw_cfg) would be a good idea.
Huh? As far I know we generate device trees in qemu instead of expecting pseries firmware compile them from fw_cfg information.
It depends on what firmware you are using.
Of course. On archs which don't use device trees in the first place it doesn't make sense.
We don't really generate device trees in general in QEMU.
pseries does (thats why the hard libfdt dependency if you want pseries support). arm wants move into that direction too.
As Peter mentioned, in an ideal world we'd generate them from the QOM graph.
That should happen in the firmware and it could be enabled by adding just a couple fw_cfg commands to navigate the QOM graph (analogs to qom-list and qom-get in QMP).
I don't think Peter intended to imply *that* ...