linux-kernel - [PATCH RFC v3 2/2] pmdomain: core: add support for subdomains using power-domain-map

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Message-Id: <20250613-pmdomain-hierarchy-onecell-v3-2-5c770676fce7@baylibre.com>
Date: Fri, 13 Jun 2025 15:39:28 -0700
From: Kevin Hilman <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
Subject: [PATCH RFC v3 2/2] pmdomain: core: add support for subdomains
 using power-domain-map

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

Add more generic support for hierarchy by using nexus node
maps (c.f. section 2.5.1 of the DT spec.)

For example, we could describe SCMI PM domains with multiple parents
domains (MAIN_PD and WKUP_PD) like this:

    scmi_pds: protocol@11 {
        reg = <0x11>;
        #power-domain-cells = <1>;

        power-domain-map = <15 &MAIN_PD>,
                           <19 &WKUP_PD>;
    };

which should mean that <&scmi_pds 15> is a subdomain of MAIN_PD and
<&scmi_pds 19> is a subdomain of WKUP_PD.

IOW, given an SCMI device which uses SCMI PM domains:

   main_timer0: timer@...0000 {
      power-domains = <&scmi_pds 15>;
   };

it already implies that main_timer0 is PM domain <&scmi_pds 15>

With the new map, this *also* now implies <&scmi_pds 15> is a
subdomain of MAIN_PD.

Signed-off-by: Kevin Hilman <khilman@...libre.com>
---
 drivers/pmdomain/core.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/drivers/pmdomain/core.c b/drivers/pmdomain/core.c
index d6c1ddb807b2..adf022b45d95 100644
--- a/drivers/pmdomain/core.c
+++ b/drivers/pmdomain/core.c
@@ -2998,8 +2998,8 @@ static int __genpd_dev_pm_attach(struct device *dev, struct device *base_dev,
 				 unsigned int index, unsigned int num_domains,
 				 bool power_on)
 {
-	struct of_phandle_args pd_args;
-	struct generic_pm_domain *pd;
+	struct of_phandle_args pd_args, parent_args;
+	struct generic_pm_domain *pd, *parent_pd = NULL;
 	int ret;
 
 	ret = of_parse_phandle_with_args(dev->of_node, "power-domains",
@@ -3039,6 +3039,22 @@ static int __genpd_dev_pm_attach(struct device *dev, struct device *base_dev,
 			goto err;
 	}
 
+	/*
+	 * Check for power-domain-map, which implies the primary
+	 * power-doamin is a subdomain of the parent found in the map.
+	 */
+	ret = of_parse_phandle_with_args_map(dev->of_node, "power-domains",
+					     "power-domain", index, &parent_args);
+	if (!ret && (pd_args.np != parent_args.np)) {
+		parent_pd = genpd_get_from_provider(&parent_args);
+		of_node_put(parent_args.np);
+
+		ret = pm_genpd_add_subdomain(parent_pd, pd);
+		if (!ret)
+			dev_dbg(dev, "adding PM domain %s as subdomain of %s\n",
+				pd->name, parent_pd->name);
+	}
+
 	ret = genpd_set_required_opp(dev, index);
 	if (ret)
 		goto err;
@@ -3056,6 +3072,8 @@ static int __genpd_dev_pm_attach(struct device *dev, struct device *base_dev,
 			dev_gpd_data(dev)->default_pstate = 0;
 		}
 
+		if (parent_pd)
+			pm_genpd_remove_subdomain(parent_pd, pd);
 		genpd_remove_device(pd, dev);
 		return -EPROBE_DEFER;
 	}
@@ -3063,6 +3081,8 @@ static int __genpd_dev_pm_attach(struct device *dev, struct device *base_dev,
 	return 1;
 
 err:
+	if (parent_pd)
+		pm_genpd_remove_subdomain(parent_pd, pd);
 	genpd_remove_device(pd, dev);
 	return ret;
 }

-- 
2.49.0