On Mon, Dec 02, 2024 at 08:18:22AM -0600, Rob Herring wrote: > On Wed, Nov 27, 2024 at 3:47 PM Segher Boessenkool > <segher@xxxxxxxxxxxxxxxxxxx> wrote: > > On Tue, Nov 26, 2024 at 02:36:32PM +1100, Michael Ellerman wrote: > > > Michael Ellerman <mpe@xxxxxxxxxxxxxx> writes: > > > > "Rob Herring (Arm)" <robh@xxxxxxxxxx> writes: > > > >> 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@xxxxxxxxxxxxxx/ > > > > 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. ? Almost all architectures (that run Linux) use 64-bit addressing, both 32-bit and 64-bit architectures. > 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. The former is correct. The latter makes no sense at all! The whole point of the "bus" abstraction is that you get a new addressing domain there. Yes, these days you numerically find it most often with PCI sub-domains, but those are boring. In most cases you *do* have different adressing on your child busses, and even if the addressing is the same, addresses on the child bus are not normally a subset of those on the parent bus. > > 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). So *always* use the OF definition, at least on OF systems? Where everything is meant to conform, but conform to OF, not conform to this "OF-like-but-very-different-in-crucial-spots" thing :-) Segher
