Rob Herring [off-list ref] writes:

On Thu, Jan 22, 2026 at 05:14:00PM -0800, Kevin Hilman (TI) wrote:

quoted

Add of_genpd_[add|remove]_subdomain_map() helper functions to support
hierarchical PM domains defined by using power-domains-map

power-domain-map. No 's'.

quoted

property (c.f. nexus node maps in DT spec, section 2.5.1).

This enables PM domain providers with #power-domain-cells > 0 to
establish subdomain relationships via the power-domain-map property,
which was not previously possible.

These new helper functions:
- uses an OF helper to iterate to over entries in power-domain-map
- For each mapped entry: extracts child specifier, resolves parent phandle,
  extracts parent specifier args, and establishes subdomain relationship
- Calls genpd_[add|remove]_subdomain() with proper gpd_list_lock mutex protection

Example from k3-am62l.dtsi:

  scmi_pds: protocol@11 {
      #power-domain-cells = <1>;
      power-domain-map = <15 &MAIN_PD>,  /* TIMER0 */
                         <19 &WKUP_PD>;  /* WKUP_TIMER0 */
  };

  MAIN_PD: power-controller-main {
      #power-domain-cells = <0>;
  };

  WKUP_PD: power-controller-main {
      #power-domain-cells = <0>;
  };

This allows SCMI power domain 15 to become a subdomain of MAIN_PD, and
domain 19 to become a subdomain of WKUP_PD.

One concern I have here is generally *-map is transparent meaning when 
you lookup <&scmi_pds 15>, &MAIN_PD is returned as the provider. It's 
also possible to have a map point to another map until you get to the 
final provider. The only way we have to support both behaviors is the 
consumer has to specify (i.e. with of_parse_phandle_with_args_map() vs. 
of_parse_phandle_with_args()), but the consumer shouldn't really know 
this detail.

Maybe a transparent map of power-domains would never make sense. IDK. If 
so, then there's not really any issue since the pmdomain core handles 
everyone the same way.

I don't really know enough about potential usage of maps to know if
there's ever a usecase for transparent maps.  However, the problem I'm
trying to solve is less about transparent maps, and more about
describing hierarchy in a situation where "leaf" domains of the same
type (e.g. SCMI) can have different parent domains.

When I first proposed this[1], I didn't use a map, but you suggested I
try using a map[2].  So I'm not sure if I misunderstood what you
proposed, or if now that you see it implemented, you're second guessing if
the map is the right approach.

Kevin

[1] https://lore.kernel.org/r/20250528-pmdomain-hierarchy-onecell-v1-1-851780700c68@baylibre.com (local)
[2] https://lore.kernel.org/r/20250528203532.GA704342-robh@kernel.org (local)