linux-kernel - [PATCH RFC v4 1/2] pmdomain: core: support domain hierarchy via power-domain-map

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Message-Id: <20251119-pmdomain-hierarchy-onecell-v4-1-f25a1d5022f8@baylibre.com>
Date: Wed, 19 Nov 2025 16:58:45 -0800
From: "Kevin Hilman (TI.com)" <khilman@...libre.com>
To: Ulf Hansson <ulf.hansson@...aro.org>, Rob Herring <robh@...nel.org>, 
 Krzysztof Kozlowski <krzk+dt@...nel.org>
Cc: devicetree@...r.kernel.org, linux-pm@...r.kernel.org, 
 arm-scmi@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Kevin Hilman <khilman@...libre.com>
Subject: [PATCH RFC v4 1/2] pmdomain: core: support domain hierarchy via
 power-domain-map

Add of_genpd_add_subdomain_map() helper function to support
hierarchical PM domains defined by using power-domains-map
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.

This new helper function
- 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
- Uses genpd_add_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.

Signed-off-by: Kevin Hilman (TI.com) <khilman@...libre.com>
---
 drivers/pmdomain/core.c   | 64 ++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/pm_domain.h |  9 +++++++
 2 files changed, 73 insertions(+)

diff --git a/drivers/pmdomain/core.c b/drivers/pmdomain/core.c
index 61c2277c9ce3..592e9126896c 100644
--- a/drivers/pmdomain/core.c
+++ b/drivers/pmdomain/core.c
@@ -3483,6 +3483,70 @@ int of_genpd_parse_idle_states(struct device_node *dn,
 }
 EXPORT_SYMBOL_GPL(of_genpd_parse_idle_states);
 
+int of_genpd_add_subdomain_map(struct device_node *np,
+			       struct genpd_onecell_data *data)
+{
+	struct generic_pm_domain *genpd, *parent_genpd;
+	struct of_phandle_args child_args, parent_args;
+	int index = 0;
+	int ret = 0;
+	u32 child_index;
+
+	if (!np || !data)
+		return -EINVAL;
+
+	/* Iterate through power-domain-map entries using the OF helper */
+	while (!of_parse_map_iter(np, "power-domain", &index,
+				   &child_args, &parent_args)) {
+		/* Extract the child domain index from the child specifier */
+		if (child_args.args_count < 1) {
+			of_node_put(parent_args.np);
+			ret = -EINVAL;
+			break;
+		}
+		child_index = child_args.args[0];
+
+		/* Validate child domain index */
+		if (child_index >= data->num_domains) {
+			of_node_put(parent_args.np);
+			continue;
+		}
+
+		genpd = data->domains[child_index];
+		if (!genpd) {
+			of_node_put(parent_args.np);
+			continue;
+		}
+
+		/* Get parent power domain from provider and establish subdomain relationship */
+		mutex_lock(&gpd_list_lock);
+
+		parent_genpd = genpd_get_from_provider(&parent_args);
+		if (IS_ERR(parent_genpd)) {
+			mutex_unlock(&gpd_list_lock);
+			of_node_put(parent_args.np);
+			ret = PTR_ERR(parent_genpd);
+			dev_err(&genpd->dev, "failed to get parent domain: %d\n", ret);
+			break;
+		}
+
+		ret = genpd_add_subdomain(parent_genpd, genpd);
+		mutex_unlock(&gpd_list_lock);
+		of_node_put(parent_args.np);
+
+		if (ret) {
+			dev_err(&genpd->dev, "failed to add as subdomain of %s: %d\n",
+				parent_genpd->name, ret);
+			break;
+		}
+
+		dev_info(&genpd->dev, "added as subdomain of %s\n",
+			parent_genpd->name);
+	}
+
+	return ret;
+}
+
 /**
  * of_genpd_sync_state() - A common sync_state function for genpd providers
  * @np: The device node the genpd provider is associated with.
diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
index f67a2cb7d781..3585acb89b83 100644
--- a/include/linux/pm_domain.h
+++ b/include/linux/pm_domain.h
@@ -462,6 +462,8 @@ int of_genpd_add_subdomain(const struct of_phandle_args *parent_spec,
 int of_genpd_remove_subdomain(const struct of_phandle_args *parent_spec,
 			      const struct of_phandle_args *subdomain_spec);
 struct generic_pm_domain *of_genpd_remove_last(struct device_node *np);
+int of_genpd_add_subdomain_map(struct device_node *np,
+			       struct genpd_onecell_data *data);
 int of_genpd_parse_idle_states(struct device_node *dn,
 			       struct genpd_power_state **states, int *n);
 void of_genpd_sync_state(struct device_node *np);
@@ -504,6 +506,13 @@ static inline int of_genpd_remove_subdomain(const struct of_phandle_args *parent
 	return -ENODEV;
 }
 
+static int of_genpd_add_subdomain_map(struct device_node *np,
+				      struct generic_pm_domain *genpd,
+				      int index)
+{
+	return -ENODEV;
+}
+
 static inline int of_genpd_parse_idle_states(struct device_node *dn,
 			struct genpd_power_state **states, int *n)
 {

-- 
2.51.0