Re: [PATCH 1/5] of: add infra for finding CPU id from phandle

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

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;