Re: Ranges - Intended use case

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On Thu, Feb 12, 2026 at 01:24:20PM -0600, Rob Herring wrote:
> On Thu, Feb 12, 2026 at 9:33=E2=80=AFAM Yao Zi <[email protected]> wrote:
> >
> > On Thu, Feb 12, 2026 at 01:14:33PM +0000, Kyle Bonnici wrote:
> > > Hi
> > >
> > > I have been trying to understand how ranges should/should not be used.
> > >
> > > Looking at the spec
> > >
> > > > The ranges property provides a means of defining a mapping or trans=
lation between the address space of the
> > > bus (the child address space) and the address space of the bus node=
=E2=80=99s parent (the parent address space).
> > >
> > > This to me the spec leave some space for interpretation on if ranges =
should be used on just buses or not. Below are some examples to try to get =
a better understanding.
> >
> > I'd like to say ranges literally specifies the translation process
> > between the children address space and the parent one, regardless
> > whether the parent is a "bus".
>=20
> Yes.
>=20
> To put it simply, "ranges" should be used whenever the child nodes
> have memory-mapped CPU addresses.

That's the most common case, but others exist.  You can encode cases
where a device's registers are mapped into its parent's bus address
space, but that parent address space is never mapped into the CPU MMIO
space.

--=20
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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