On Wed, Nov 27, 2024 at 3:47 PM Segher Boessenkool
[off-list ref] wrote:

On Tue, Nov 26, 2024 at 02:36:32PM +1100, Michael Ellerman wrote:

quoted

Michael Ellerman [off-list ref] writes:

quoted

"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)

The Open Firmware specification is extremely clear that a "missing"
"#size-cells" property means this bus has the default value of 1.

And the default for #address-cells is 2, but yet every architecture
except Sparc has that wrong.

If I have a node without #size-cells, is the default of 1 used or do
we check parent nodes? My read of the spec would be the former, but
the kernel does the latter.

https://www.openfirmware.info/data/docs/of1275.pdf (page 186).

DTC or FDT might want to do things differently, but expecting decades
older stuff to conform to its ill-conceived unnecessarily super wordy
stuff is, well, not a plan that is likely to work very well :-)

That is not the intention. The intention is to identify what doesn't
conform and exclude those systems from this check (or apply a fixup if
that works).

Rob