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

[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@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@baylibre.com>

[PATCH v3 1/3] dt-bindings: power: Add power-domains-child-ids property

[Kevin Hilman (TI)]

Add binding documentation for the new power-domains-child-ids property,
which works in conjunction with the existing power-domains property to
establish parent-child relationships between a multi-domain power domain
provider and external parent domains.

Each element in the uint32 array identifies the child domain
ID (index) within the provider that should be made a child domain of
the corresponding phandle entry in power-domains. The two arrays must
have the same number of elements.

Signed-off-by: Kevin Hilman (TI) <khilman@baylibre.com>
---
 Documentation/devicetree/bindings/power/power-domain.yaml | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/Documentation/devicetree/bindings/power/power-domain.yaml b/Documentation/devicetree/bindings/power/power-domain.yaml
index b1147dbf2e73..163b0af158fd 100644
--- a/Documentation/devicetree/bindings/power/power-domain.yaml
+++ b/Documentation/devicetree/bindings/power/power-domain.yaml
@@ -68,6 +68,21 @@ properties:
       by the given provider should be subdomains of the domain specified
       by this binding.
 
+  power-domains-child-ids:
+    $ref: /schemas/types.yaml#/definitions/uint32-array
+    description:
+      An array of child domain IDs that correspond to the power-domains
+      property. This property is only applicable to power domain providers
+      with "#power-domain-cells" > 0 (i.e., providers that supply multiple
+      power domains). It specifies which of the provider's child domains
+      should be associated with each parent domain listed in the power-domains
+      property. The number of elements in this array must match the number of
+      phandles in the power-domains property. Each element specifies the child
+      domain ID (index) that should be made a child domain of the corresponding
+      parent domain. This enables hierarchical power domain structures where
+      different child domains from the same provider can have different
+      parent domains.
+
 required:
   - "#power-domain-cells"
 
@@ -133,3 +148,22 @@ examples:
             min-residency-us = <7000>;
         };
     };
+
+  - |
+    // Example: SCMI domain 15 -> MAIN_PD, SCMI domain 19 -> WKUP_PD
+    MAIN_PD: power-controller-main {
+        compatible = "foo,power-controller";
+        #power-domain-cells = <0>;
+    };
+
+    WKUP_PD: power-controller-wkup {
+        compatible = "foo,power-controller";
+        #power-domain-cells = <0>;
+    };
+
+    scmi_pds: power-controller-scmi {
+        compatible = "foo,power-controller";
+        #power-domain-cells = <1>;
+        power-domains = <&MAIN_PD>, <&WKUP_PD>;
+        power-domains-child-ids = <15>, <19>;
+    };

-- 
2.51.0

[PATCH v3 2/3] pmdomain: core: add support for power-domains-child-ids

[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.

For example, an SCMI PM domain provider has multiple domains, each of
which might be a child of diffeent parent domains. In this example,
the parent domains are MAIN_PD and WKUP_PD:

    scmi_pds: protocol@11 {
        reg = <0x11>;
        #power-domain-cells = <1>;
        power-domains = <&MAIN_PD>, <&WKUP_PD>;
        power-domains-child-ids = <15>, <19>;
    };

With this example using the new property, SCMI PM domain 15 becomes a
child domain of MAIN_PD, and SCMI domain 19 becomes a child domain of
WKUP_PD.

To support this feature, add two new core functions

- of_genpd_add_child_ids()
- of_genpd_remove_child_ids()

which can be called by pmdomain providers to add/remove child domains
if they support the new property power-domains-child-ids.

The add function is "all or nothing".  If it cannot add all of the
child domains in the list, it will unwind any additions already made
and report a failure.

Signed-off-by: Kevin Hilman (TI) <khilman@baylibre.com>
---
 drivers/pmdomain/core.c   | 167 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/pm_domain.h |  16 ++++++++++++++++
 2 files changed, 183 insertions(+)

diff --git a/drivers/pmdomain/core.c b/drivers/pmdomain/core.c
index 61c2277c9ce3..97498a37336d 100644
--- a/drivers/pmdomain/core.c
+++ b/drivers/pmdomain/core.c
@@ -2909,6 +2909,173 @@ static struct generic_pm_domain *genpd_get_from_provider(
 	return genpd;
 }
 
+/**
+ * of_genpd_add_child_ids() - Parse power-domains-child-ids property
+ * @np: Device node pointer associated with the PM domain provider.
+ * @data: Pointer to the onecell data associated with the PM domain provider.
+ *
+ * Parse the power-domains and power-domains-child-ids properties to establish
+ * parent-child relationships for PM domains. The power-domains property lists
+ * parent domains, and power-domains-child-ids lists which child domain IDs
+ * should be associated with each parent.
+ *
+ * Uses "all or nothing" semantics: either all relationships are established
+ * successfully, or none are (any partially-added relationships are unwound
+ * on error).
+ *
+ * Returns the number of parent-child relationships established on success,
+ * 0 if the properties don't exist, or a negative error code on failure.
+ */
+int of_genpd_add_child_ids(struct device_node *np,
+			   struct genpd_onecell_data *data)
+{
+	struct of_phandle_args parent_args;
+	struct generic_pm_domain *parent_genpd, *child_genpd;
+	struct generic_pm_domain **pairs; /* pairs[2*i]=parent, pairs[2*i+1]=child */
+	u32 child_id;
+	int i, ret, count, child_count, added = 0;
+
+	/* Check if both properties exist */
+	count = of_count_phandle_with_args(np, "power-domains", "#power-domain-cells");
+	if (count <= 0)
+		return 0;
+
+	child_count = of_property_count_u32_elems(np, "power-domains-child-ids");
+	if (child_count < 0)
+		return 0;
+	if (child_count != count)
+		return -EINVAL;
+
+	/* Allocate tracking array for error unwind (parent/child pairs) */
+	pairs = kmalloc_array(count * 2, sizeof(*pairs), GFP_KERNEL);
+	if (!pairs)
+		return -ENOMEM;
+
+	for (i = 0; i < count; i++) {
+		ret = of_property_read_u32_index(np, "power-domains-child-ids",
+						 i, &child_id);
+		if (ret)
+			goto err_unwind;
+
+		/* Validate child ID is within bounds */
+		if (child_id >= data->num_domains) {
+			pr_err("Child ID %u out of bounds (max %u) for %pOF\n",
+			       child_id, data->num_domains - 1, np);
+			ret = -EINVAL;
+			goto err_unwind;
+		}
+
+		/* Get the child domain */
+		child_genpd = data->domains[child_id];
+		if (!child_genpd) {
+			pr_err("Child domain %u is NULL for %pOF\n", child_id, np);
+			ret = -EINVAL;
+			goto err_unwind;
+		}
+
+		ret = of_parse_phandle_with_args(np, "power-domains",
+						 "#power-domain-cells", i,
+						 &parent_args);
+		if (ret)
+			goto err_unwind;
+
+		/* Get the parent domain */
+		parent_genpd = genpd_get_from_provider(&parent_args);
+		of_node_put(parent_args.np);
+		if (IS_ERR(parent_genpd)) {
+			pr_err("Failed to get parent domain for %pOF: %ld\n",
+			       np, PTR_ERR(parent_genpd));
+			ret = PTR_ERR(parent_genpd);
+			goto err_unwind;
+		}
+
+		/* Establish parent-child relationship */
+		ret = pm_genpd_add_subdomain(parent_genpd, child_genpd);
+		if (ret) {
+			pr_err("Failed to add child domain %u to parent in %pOF: %d\n",
+			       child_id, np, ret);
+			goto err_unwind;
+		}
+
+		/* Track for potential unwind */
+		pairs[2 * added] = parent_genpd;
+		pairs[2 * added + 1] = child_genpd;
+		added++;
+
+		pr_debug("Added child domain %u (%s) to parent %s for %pOF\n",
+			 child_id, child_genpd->name, parent_genpd->name, np);
+	}
+
+	kfree(pairs);
+	return count;
+
+err_unwind:
+	/* Reverse all previously established relationships */
+	while (added-- > 0)
+		pm_genpd_remove_subdomain(pairs[2 * added], pairs[2 * added + 1]);
+	kfree(pairs);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(of_genpd_add_child_ids);
+
+/**
+ * of_genpd_remove_child_ids() - Remove parent-child PM domain relationships
+ * @np: Device node pointer associated with the PM domain provider.
+ * @data: Pointer to the onecell data associated with the PM domain provider.
+ *
+ * Reverses the effect of of_genpd_add_child_ids() by parsing the same
+ * power-domains and power-domains-child-ids properties and calling
+ * pm_genpd_remove_subdomain() for each established relationship.
+ *
+ * Returns 0 on success, -ENOENT if properties don't exist, or negative error
+ * code on failure.
+ */
+int of_genpd_remove_child_ids(struct device_node *np,
+			   struct genpd_onecell_data *data)
+{
+	struct of_phandle_args parent_args;
+	struct generic_pm_domain *parent_genpd, *child_genpd;
+	u32 child_id;
+	int i, ret, count, child_count;
+
+	/* Check if both properties exist */
+	count = of_count_phandle_with_args(np, "power-domains", "#power-domain-cells");
+	if (count <= 0)
+		return -ENOENT;
+
+	child_count = of_property_count_u32_elems(np, "power-domains-child-ids");
+	if (child_count < 0)
+		return -ENOENT;
+	if (child_count != count)
+		return -EINVAL;
+
+	for (i = 0; i < count; i++) {
+		if (of_property_read_u32_index(np, "power-domains-child-ids",
+					       i, &child_id))
+			continue;
+
+		if (child_id >= data->num_domains || !data->domains[child_id])
+			continue;
+
+		ret = of_parse_phandle_with_args(np, "power-domains",
+						 "#power-domain-cells", i,
+						 &parent_args);
+		if (ret)
+			continue;
+
+		parent_genpd = genpd_get_from_provider(&parent_args);
+		of_node_put(parent_args.np);
+		if (IS_ERR(parent_genpd))
+			continue;
+
+		child_genpd = data->domains[child_id];
+		pm_genpd_remove_subdomain(parent_genpd, child_genpd);
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(of_genpd_remove_child_ids);
+
 /**
  * of_genpd_add_device() - Add a device to an I/O PM domain
  * @genpdspec: OF phandle args to use for look-up PM domain
diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
index f67a2cb7d781..b44615d79af6 100644
--- a/include/linux/pm_domain.h
+++ b/include/linux/pm_domain.h
@@ -465,6 +465,10 @@ struct generic_pm_domain *of_genpd_remove_last(struct device_node *np);
 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);
+int of_genpd_add_child_ids(struct device_node *np,
+			   struct genpd_onecell_data *data);
+int of_genpd_remove_child_ids(struct device_node *np,
+			      struct genpd_onecell_data *data);
 
 int genpd_dev_pm_attach(struct device *dev);
 struct device *genpd_dev_pm_attach_by_id(struct device *dev,
@@ -534,6 +538,18 @@ struct generic_pm_domain *of_genpd_remove_last(struct device_node *np)
 {
 	return ERR_PTR(-EOPNOTSUPP);
 }
+
+static inline int of_genpd_add_child_ids(struct device_node *np,
+					 struct genpd_onecell_data *data)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int of_genpd_remove_child_ids(struct device_node *np,
+					    struct genpd_onecell_data *data)
+{
+	return -EOPNOTSUPP;
+}
 #endif /* CONFIG_PM_GENERIC_DOMAINS_OF */
 
 #ifdef CONFIG_PM

-- 
2.51.0

[PATCH v3 3/3] pmdomain: arm_scmi: add support for domain hierarchies

[Kevin Hilman (TI)]

After primary SCMI pmdomain is created, use new of_genpd helper which
checks for child domain mappings defined in power-domains-child-ids.

Also remove any child domain mappings when SCMI domain is removed.

Signed-off-by: Kevin Hilman (TI) <khilman@baylibre.com>
---
 drivers/pmdomain/arm/scmi_pm_domain.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/pmdomain/arm/scmi_pm_domain.c b/drivers/pmdomain/arm/scmi_pm_domain.c
index b5e2ffd5ea64..66dcf2e687a8 100644
--- a/drivers/pmdomain/arm/scmi_pm_domain.c
+++ b/drivers/pmdomain/arm/scmi_pm_domain.c
@@ -114,6 +114,14 @@ static int scmi_pm_domain_probe(struct scmi_device *sdev)
 
 	dev_set_drvdata(dev, scmi_pd_data);
 
+	/*
+	 * Parse (optional) power-domains-child-ids property to
+	 * establish parent-child relationships
+	 */
+	ret = of_genpd_add_child_ids(np, scmi_pd_data);
+	if (ret < 0)
+		dev_err(dev, "Failed to add child domain hierarchy: %d\n", ret);
+
 	return 0;
 err_rm_genpds:
 	for (i = num_domains - 1; i >= 0; i--)
@@ -129,9 +137,13 @@ static void scmi_pm_domain_remove(struct scmi_device *sdev)
 	struct device *dev = &sdev->dev;
 	struct device_node *np = dev->of_node;
 
+	scmi_pd_data = dev_get_drvdata(dev);
+
+	/* Remove any parent-child relationships established at probe time */
+	of_genpd_remove_child_ids(np, scmi_pd_data);
+
 	of_genpd_del_provider(np);
 
-	scmi_pd_data = dev_get_drvdata(dev);
 	for (i = 0; i < scmi_pd_data->num_domains; i++) {
 		if (!scmi_pd_data->domains[i])
 			continue;

-- 
2.51.0

Re: [PATCH v3 1/3] dt-bindings: power: Add power-domains-child-ids property

[Rob Herring]

On Mon, Apr 20, 2026 at 04:51:17PM -0700, Kevin Hilman (TI) wrote:
> Add binding documentation for the new power-domains-child-ids property,
> which works in conjunction with the existing power-domains property to
> establish parent-child relationships between a multi-domain power domain
> provider and external parent domains.
> 
> Each element in the uint32 array identifies the child domain
> ID (index) within the provider that should be made a child domain of
> the corresponding phandle entry in power-domains. The two arrays must
> have the same number of elements.
> 
> Signed-off-by: Kevin Hilman (TI) <khilman@baylibre.com>

Missing my Reviewed-by.

Re: [PATCH v3 1/3] dt-bindings: power: Add power-domains-child-ids property

[Kevin Hilman]

Rob Herring <robh@kernel.org> writes:

> On Mon, Apr 20, 2026 at 04:51:17PM -0700, Kevin Hilman (TI) wrote:
>> Add binding documentation for the new power-domains-child-ids property,
>> which works in conjunction with the existing power-domains property to
>> establish parent-child relationships between a multi-domain power domain
>> provider and external parent domains.
>> 
>> Each element in the uint32 array identifies the child domain
>> ID (index) within the provider that should be made a child domain of
>> the corresponding phandle entry in power-domains. The two arrays must
>> have the same number of elements.
>> 
>> Signed-off-by: Kevin Hilman (TI) <khilman@baylibre.com>
>
> Missing my Reviewed-by.

Oops, I thought I had grabbed it with b4, but I didn't.  Sorry.

Kevin