of: base: Add of_get_cpu_state_node() to get idle states for a CPU node

The CPU's idle state nodes are currently parsed at the common cpuidle DT
library, but also when initializing data for specific CPU idle operations,
as in the PSCI cpuidle driver case and qcom-spm cpuidle case.

To avoid open-coding, let's introduce of_get_cpu_state_node(), which takes
the device node for the CPU and the index to the requested idle state node,
as in-parameters. In case a corresponding idle state node is found, it
returns the node with the refcount incremented for it, else it returns
NULL.

Moreover, for PSCI there are two options to describe the CPU's idle states
[1], either via a flattened description or a hierarchical layout. Hence,
let's take both options into account.

[1] Documentation/devicetree/bindings/arm/psci.yaml
Suggested-by: Sudeep Holla <sudeep.holla@arm.com>
Co-developed-by: Lina Iyer <lina.iyer@linaro.org>
Signed-off-by: Lina Iyer <lina.iyer@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/of/base.c

@@ -489,6 +489,42 @@ int of_cpu_node_to_id(struct device_node *cpu_node)
 }
 EXPORT_SYMBOL(of_cpu_node_to_id);
 
+/**
+ * of_get_cpu_state_node - Get CPU's idle state node at the given index
+ *
+ * @cpu_node: The device node for the CPU
+ * @index: The index in the list of the idle states
+ *
+ * Two generic methods can be used to describe a CPU's idle states, either via
+ * a flattened description through the "cpu-idle-states" binding or via the
+ * hierarchical layout, using the "power-domains" and the "domain-idle-states"
+ * bindings. This function check for both and returns the idle state node for
+ * the requested index.
+ *
+ * In case an idle state node is found at @index, the refcount is incremented
+ * for it, so call of_node_put() on it when done. Returns NULL if not found.
+ */
+struct device_node *of_get_cpu_state_node(struct device_node *cpu_node,
+					  int index)
+{
+	struct of_phandle_args args;
+	int err;
+
+	err = of_parse_phandle_with_args(cpu_node, "power-domains",
+					"#power-domain-cells", 0, &args);
+	if (!err) {
+		struct device_node *state_node =
+			of_parse_phandle(args.np, "domain-idle-states", index);
+
+		of_node_put(args.np);
+		if (state_node)
+			return state_node;
+	}
+
+	return of_parse_phandle(cpu_node, "cpu-idle-states", index);
+}
+EXPORT_SYMBOL(of_get_cpu_state_node);
+
 /**
  * __of_device_is_compatible() - Check if the node matches given constraints
  * @device: pointer to node

include/linux/of.h

@@ -351,6 +351,8 @@ extern const void *of_get_property(const struct device_node *node,
 				int *lenp);
 extern struct device_node *of_get_cpu_node(int cpu, unsigned int *thread);
 extern struct device_node *of_get_next_cpu_node(struct device_node *prev);
+extern struct device_node *of_get_cpu_state_node(struct device_node *cpu_node,
+						 int index);
 
 #define for_each_property_of_node(dn, pp) \
 	for (pp = dn->properties; pp != NULL; pp = pp->next)
@@ -765,6 +767,12 @@ static inline struct device_node *of_get_next_cpu_node(struct device_node *prev)
 	return NULL;
 }
 
+static inline struct device_node *of_get_cpu_state_node(struct device_node *cpu_node,
+					int index)
+{
+	return NULL;
+}
+
 static inline int of_n_addr_cells(struct device_node *np)
 {
 	return 0;