Re: Ranges - Intended use case

Yao Zi
2026-02-12T15:33:44Z

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 translation between the address space of the
> bus (the child address space) and the address space of the bus node’s 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".

For example, reserved-memory nodes aren't really "buses", but often
come with ranges property, as shown in the example of dt-schema[1].

However it might be a signature of bad device-tree model designs if you
have to use a ranges property for a random non-bus node.

>
> ```
> / {
> foo { // not a bus
> #address-cells = <1>;
> #size-cells = <1>;
> ranges; // does this ranges have any meaning?

I'd like to say, yes.

> bar@10 {
> reg<0x10 …>
> };
> };
> };
> ```
>
> ```
> / {
> foo { // not a bus
> #address-cells = <1>;
> #size-cells = <1>;
> reg = <0x100 0x50>;
> ranges = <0x0 0x100 0x50>; // is this an intended use case?

Depending on what the child node represents, but IMHO it comes with a
clear meaning.

> bar@10 {
> reg<0x10 …> // hence abs address is 0x110.
> };
> };
> };
> ```
>
> ```
> / {
> foo { // bus
> compatible = <simple-bus>;
> #address-cells = <1>;
> #size-cells = <1>;
> ranges; // this I understand to declare that children will have direct mapping
>
> bar {
> ranges; // is this needed? Or is it implied that the foobar is in the same address space of bar?

It's necessary. I don't think ranges property is ever implied.

> foobar@10 {
> reg<0x10 …> // hence abs address is 0x10.
> };
> };
> };
> };
> ```
>
> ```
> / {
> soc { // bus
> compatible = <simple-bus>;
> #address-cells = <1>;
> #size-cells = <1>;
> ranges; // this I understand to declare that children will have direct mapping
>
> flash@1000 {
> reg<0x1000 …>
> ranges = <0x0 0x1000 …>;
>
> partitions {
> ranges; // is this needed? Or is it implied that the partition1 is in the same address space of partitions?

Personally I think it SHOULD be needed, though existing dt-bindings for
fixed partition layout don't enforce such.

I'm not very familiar with flash partitions and their dt patterns, so
will leave the question for others :)

> partition1@10 {
> reg<0x10 …> // hence abs address is 0x1010.
> };
> };
> };
> };
> };
> ```
>
> Looking forward to explanations on this topic to extend my understanding of devicetree
>
> Regards
> Kyle

Best regards,
Yao Zi

[1]: https://github.com/devicetree-org/dt-schema/blob/d16dc68b093e59ec4ae6a32a2e1179cb9cc0fada/dtschema/schemas/reserved-memory/reserved-memory.yaml#L147