[PATCH v3 0/3] pmdomain: core: add support for domain hierarchies in DT

[Kevin Hilman (TI)]

Currently, PM domains can only support hierarchy for simple
providers (e.g. ones with #power-domain-cells = 0).

Add support for oncell providers as well by adding a new property
`power-domains-child-ids` to describe the parent/child relationship.

Also adds the first user of the new API: the Arm SCMI PM domain driver.

Signed-off-by: Kevin Hilman (TI) <khilman at baylibre.com>
---
Changes in v3:
- cleanup return codes for add_child_ids()
  - < 0: error
  - zero means no child domains present
  - > 0: number of child domains added
- arm_scmi: adopt to new return codes (only <0 is an error)
- Link to v2: https://patch.msgid.link/20260410-topic-lpm-pmdomain-child-ids-v2-0-83396e4b5f8b@baylibre.com

Changes compared to initial RFC[2]
- dropped RFC
- rewrote the parse/add function to use iterators/helpers from of.h
- add a remove function for cleanup
- use child domain language instead of subdomain

This idea was previously discussed on the arm-scmi mailing list[1]
where this approach was proposed by Ulf, and then an initial RFC[2]
implementation was made.  From there, it was suggested by Rob[3] to
use a nexus node map instead, which led to several more versions
attempting to implement that, culminating in v5[4], where Rob and
Geert then had second thoughts about the power-domain-map approach.

Therefore, I've gone back to the approach in the initial RFC[2] to use
the child-ids approach.

[1] https://lore.kernel.org/arm-scmi/CAPDyKFo_P129sVirHHYjOQT+QUmpymcRJme9obzKJeRgO7B-1A@mail.gmail.com/
[2] https://lore.kernel.org/all/20250528-pmdomain-hierarchy-onecell-v1-1-851780700c68@baylibre.com/
[3] https://lore.kernel.org/all/20250528203532.GA704342-robh@kernel.org/
[4] https://lore.kernel.org/r/20260122-pmdomain-hierarchy-onecell-v5-0-76855ec856bd@baylibre.com

Changes in v2:
- dt-bindings: fix warinings from make dt_binding_check
- scmi_pm_domain: switch to dev_err()
- pmdomain: core: fix locking around add/remove domains
- pmdomain: error unwind if any children fail to be added
- pmdomain: fix node reference leak
- pmdomain: ensure power-domains and child-ids properties are same
  length before iterating
- Link to v1: https://patch.msgid.link/20260310-topic-lpm-pmdomain-child-ids-v1-0-5361687a18ff@baylibre.com

---
Kevin Hilman (TI) (3):
      dt-bindings: power: Add power-domains-child-ids property
      pmdomain: core: add support for power-domains-child-ids
      pmdomain: arm_scmi: add support for domain hierarchies

 Documentation/devicetree/bindings/power/power-domain.yaml |  34 ++++++++++++++++++++++++++++++++++
 drivers/pmdomain/arm/scmi_pm_domain.c                     |  14 +++++++++++++-
 drivers/pmdomain/core.c                                   | 167 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/pm_domain.h                                 |  16 ++++++++++++++++
 4 files changed, 230 insertions(+), 1 deletion(-)
---
base-commit: f7b88edb52c8dd01b7e576390d658ae6eef0e134
change-id: 20260310-topic-lpm-pmdomain-child-ids-e3d57ae57040

Best regards,
--  
Kevin Hilman (TI) <khilman at baylibre.com>