Michael Ellerman [off-list ref] writes:

"Rob Herring (Arm)" [off-list ref] writes:

quoted

While OpenFirmware originally allowed walking parent nodes and default
root values for #address-cells and #size-cells, FDT has long required
explicit values. It's been a warning in dtc for the root node since the
beginning (2005) and for any parent node since 2007. Of course, not all
FDT uses dtc, but that should be the majority by far. The various
extracted OF devicetrees I have dating back to the 1990s (various
PowerMac, OLPC, PASemi Nemo) all have explicit root node properties.

I have various old device trees that have been given to me over the
years, and as far as I can tell they all have these properties (some of
them are partial trees so it's hard to be 100% sure).

So LGTM.

Turns out I was wrong.

The warning about #size-cells hits on some powermacs, possible fixup
patch here:

  https://lore.kernel.org/linuxppc-dev/20241126025710.591683-1-mpe@ellerman.id.au/ (local)

cheers