The CPU's idle state nodes are currently parsed at the common cpuidle DT
library, but also when initializing back-end data for the arch specific CPU
operations, as in the PSCI driver 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 ARM, there are two generic methods, to describe the CPU's
idle states, either via the flattened description through the
"cpu-idle-states" binding [1] or via the hierarchical layout, using the
"power-domains" and the "domain-idle-states" bindings [2]. Hence, let's
take both options into account.

[1]
Documentation/devicetree/bindings/arm/idle-states.txt
[2]
Documentation/devicetree/bindings/arm/psci.txt

Cc: Rob Herring <robh...@kernel.org>
Cc: devicet...@vger.kernel.org
Cc: Lina Iyer <il...@codeaurora.org>
Suggested-by: Sudeep Holla <sudeep.ho...@arm.com>
Co-developed-by: Lina Iyer <lina.i...@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hans...@linaro.org>
---
 drivers/of/base.c  | 35 +++++++++++++++++++++++++++++++++++
 include/linux/of.h |  8 ++++++++
 2 files changed, 43 insertions(+)

diff --git a/drivers/of/base.c b/drivers/of/base.c
index 848f549..97350cc 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -400,6 +400,41 @@ 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 and idle state node is found at index, the refcount 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);
+               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
  * @compat: required compatible string, NULL or "" for any match
diff --git a/include/linux/of.h b/include/linux/of.h
index 4d25e4f..15072b1 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -348,6 +348,8 @@ extern const void *of_get_property(const struct device_node 
*node,
                                const char *name,
                                int *lenp);
 extern struct device_node *of_get_cpu_node(int cpu, unsigned int *thread);
+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)
 
@@ -733,6 +735,12 @@ static inline struct device_node *of_get_cpu_node(int cpu,
        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;
-- 
2.7.4

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