Get CPU id from phandle. Many drivers get do this by getting hold of CPU
node first through a phandle and then find the CPU ID using the relevant
function. This commit encapsulates cpu node finding and improves
readability.

The API interface requires two parameters, 1) node, 2) pointer to CPU
node. API sets the pointer to the CPU node and allows the driver to play
with the CPU itself, for logging purposes for instance.

Signed-off-by: Alireza Sanaee <alireza.sanaee@huawei.com>
---
 drivers/of/cpu.c   | 29 +++++++++++++++++++++++++++++
 include/linux/of.h |  9 +++++++++
 2 files changed, 38 insertions(+)

diff --git a/drivers/of/cpu.c b/drivers/of/cpu.c
index 5214dc3d05ae..fba17994fc20 100644
--- a/drivers/of/cpu.c
+++ b/drivers/of/cpu.c
@@ -173,6 +173,35 @@ int of_cpu_node_to_id(struct device_node *cpu_node)
 }
 EXPORT_SYMBOL(of_cpu_node_to_id);
 
+/**
+ * of_cpu_phandle_to_id: Get the logical CPU number for a given device_node
+ *
+ * @node: Pointer to the device_node containing CPU phandle.
+ * @cpu_np: Pointer to the device_node for CPU.
+ * @cpu_idx: The index of the CPU in the list of CPUs.
+ *
+ * Return: The logical CPU number of the given CPU device_node or -ENODEV if
+ * the CPU is not found, or if the node is NULL, it returns -1. On success,
+ * cpu_np will always point to the retrieved CPU device_node with refcount
+ * incremented, use of_node_put() on it when done.
+ */
+int of_cpu_phandle_to_id(const struct device_node *node,
+			 struct device_node **cpu_np,
+			 uint8_t cpu_idx)
+{
+	if (!node)
+		return -1;
+
+	*cpu_np = of_parse_phandle(node, "cpu", 0);
+	if (!*cpu_np)
+		*cpu_np = of_parse_phandle(node, "cpus", cpu_idx);
+			if (!*cpu_np)
+				return -ENODEV;
+
+	return of_cpu_node_to_id(*cpu_np);
+}
+EXPORT_SYMBOL(of_cpu_phandle_to_id);
+
 /**
  * of_get_cpu_state_node - Get CPU's idle state node at the given index
  *
diff --git a/include/linux/of.h b/include/linux/of.h
index eaf0e2a2b75c..194f1cb0f6c6 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -360,6 +360,8 @@ extern const void *of_get_property(const struct device_node *node,
 extern struct device_node *of_get_cpu_node(int cpu, unsigned int *thread);
 extern struct device_node *of_cpu_device_node_get(int cpu);
 extern int of_cpu_node_to_id(struct device_node *np);
+extern int of_cpu_phandle_to_id(const struct device_node *np,
+				struct device_node **cpu_np, uint8_t cpu_idx);
 extern struct device_node *of_get_next_cpu_node(struct device_node *prev);
 extern struct device_node *of_get_cpu_state_node(const struct device_node *cpu_node,
 						 int index);
@@ -662,6 +664,13 @@ static inline int of_cpu_node_to_id(struct device_node *np)
 	return -ENODEV;
 }
 
+static inline int of_cpu_phandle_to_id(const struct device_node *np,
+				       struct device_node **cpu_np,
+				       uint8_t cpu_idx)
+{
+	return -ENODEV;
+}
+
 static inline struct device_node *of_get_next_cpu_node(struct device_node *prev)
 {
 	return NULL;
-- 
2.43.0

On Mon, 7 Jul 2025 16:04:10 +0100
Alireza Sanaee <alireza.sanaee@huawei.com> wrote:

> Get CPU id from phandle. Many drivers get do this by getting hold of CPU
> node first through a phandle and then find the CPU ID using the relevant
> function. This commit encapsulates cpu node finding and improves
> readability.
> 
> The API interface requires two parameters, 1) node, 2) pointer to CPU
> node. API sets the pointer to the CPU node and allows the driver to play
> with the CPU itself, for logging purposes for instance.
> 
> Signed-off-by: Alireza Sanaee <alireza.sanaee@huawei.com>
> ---
>  drivers/of/cpu.c   | 29 +++++++++++++++++++++++++++++
>  include/linux/of.h |  9 +++++++++
>  2 files changed, 38 insertions(+)
> 
> diff --git a/drivers/of/cpu.c b/drivers/of/cpu.c
> index 5214dc3d05ae..fba17994fc20 100644
> --- a/drivers/of/cpu.c
> +++ b/drivers/of/cpu.c
> @@ -173,6 +173,35 @@ int of_cpu_node_to_id(struct device_node *cpu_node)
>  }
>  EXPORT_SYMBOL(of_cpu_node_to_id);
>  
> +/**
> + * of_cpu_phandle_to_id: Get the logical CPU number for a given device_node
> + *
> + * @node: Pointer to the device_node containing CPU phandle.
> + * @cpu_np: Pointer to the device_node for CPU.
> + * @cpu_idx: The index of the CPU in the list of CPUs.
> + *
> + * Return: The logical CPU number of the given CPU device_node or -ENODEV if
> + * the CPU is not found, or if the node is NULL, it returns -1. On success,
> + * cpu_np will always point to the retrieved CPU device_node with refcount
> + * incremented, use of_node_put() on it when done.
> + */
> +int of_cpu_phandle_to_id(const struct device_node *node,
> +			 struct device_node **cpu_np,
> +			 uint8_t cpu_idx)
> +{
> +	if (!node)
> +		return -1;
> +
> +	*cpu_np = of_parse_phandle(node, "cpu", 0);

Gut feeling is that it would be useful to allow a NULL cpu_np
for case where they don't want the cpu device_node, just the ID.

For that you'll need a local variable to hold the device_node
then assign it or put it depending on whether cpu_np != NULL.


Maybe there are no users for that pattern though.  If that's the case
then check !node || !cpu_np for that first check. 


> +	if (!*cpu_np)
> +		*cpu_np = of_parse_phandle(node, "cpus", cpu_idx);
> +			if (!*cpu_np)
> +				return -ENODEV;
> +
> +	return of_cpu_node_to_id(*cpu_np);
> +}
> +EXPORT_SYMBOL(of_cpu_phandle_to_id);
> +
>  /**
>   * of_get_cpu_state_node - Get CPU's idle state node at the given index
>   *
> diff --git a/include/linux/of.h b/include/linux/of.h
> index eaf0e2a2b75c..194f1cb0f6c6 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -360,6 +360,8 @@ extern const void *of_get_property(const struct device_node *node,
>  extern struct device_node *of_get_cpu_node(int cpu, unsigned int *thread);
>  extern struct device_node *of_cpu_device_node_get(int cpu);
>  extern int of_cpu_node_to_id(struct device_node *np);
> +extern int of_cpu_phandle_to_id(const struct device_node *np,
> +				struct device_node **cpu_np, uint8_t cpu_idx);
>  extern struct device_node *of_get_next_cpu_node(struct device_node *prev);
>  extern struct device_node *of_get_cpu_state_node(const struct device_node *cpu_node,
>  						 int index);
> @@ -662,6 +664,13 @@ static inline int of_cpu_node_to_id(struct device_node *np)
>  	return -ENODEV;
>  }
>  
> +static inline int of_cpu_phandle_to_id(const struct device_node *np,
> +				       struct device_node **cpu_np,
> +				       uint8_t cpu_idx)
> +{
> +	return -ENODEV;
> +}
> +
>  static inline struct device_node *of_get_next_cpu_node(struct device_node *prev)
>  {
>  	return NULL;