linux-kernel - Re: [PATCH v2 1/5] of: add infra for finding CPU id from phandle

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Message-ID: <20250711103525.000022d7@huawei.com>
Date: Fri, 11 Jul 2025 10:35:25 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Alireza Sanaee <alireza.sanaee@...wei.com>
CC: <krzk@...nel.org>, <robh@...nel.org>, <coresight@...ts.linaro.org>,
	<devicetree@...r.kernel.org>, <dianders@...omium.org>,
	<james.clark@...aro.org>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <linux-perf-users@...r.kernel.org>,
	<linuxarm@...wei.com>, <mark.rutland@....com>, <mike.leach@...aro.org>,
	<ruanjinjie@...wei.com>, <saravanak@...gle.com>,
	<shameerali.kolothum.thodi@...wei.com>
Subject: Re: [PATCH v2 1/5] of: add infra for finding CPU id from phandle

On Tue, 8 Jul 2025 16:14:58 +0100
Alireza Sanaee <alireza.sanaee@...wei.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
> pointer of CPU node, 3) cpu node index. 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@...wei.com>
> ---
>  drivers/of/cpu.c   | 40 ++++++++++++++++++++++++++++++++++++++++
>  include/linux/of.h |  9 +++++++++
>  2 files changed, 49 insertions(+)
> 
> diff --git a/drivers/of/cpu.c b/drivers/of/cpu.c
> index 5214dc3d05ae..494d47470f94 100644
> --- a/drivers/of/cpu.c
> +++ b/drivers/of/cpu.c
> @@ -173,6 +173,46 @@ 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)
> +{
> +	struct device_node *local_cpu_node;
> +	int cpu;
> +
> +	if (!node)
> +		return -1;
> +
> +	local_cpu_node = of_parse_phandle(node, "cpu", 0);

Sorry - half asleep in earlier reviews. This is only valid if cpu_idx = 0 I think?

	struct device_node *local_cpu_node = NULL;

...
	if (cpu_idx == 0)
		local_cpu_node = of_parse_phandle(node, "cpu", 0);
	if (!local_cpu_node)
		local_cpu_node = of_parse_phandle(node, "cpus", cpu_idx);

Is probably the simplest implementation.
Very unlikely we'd ever call it with the combination of cpu phandle and an index
as that will be constrained by the user (currently just the DSU I think)
but we should still make the code not doing crazy things if that happens.


> +	if (!local_cpu_node)
> +		local_cpu_node = of_parse_phandle(node, "cpus", cpu_idx);
> +
> +	if (!local_cpu_node)
> +		return -ENODEV;
> +
> +	cpu = of_cpu_node_to_id(local_cpu_node);
> +
> +	if (cpu_np)
> +		*cpu_np = local_cpu_node;
> +	else
> +		of_node_put(local_cpu_node);
> +
> +	return cpu;
> +}
> +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 a62154aeda1b..717e55065d99 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -365,6 +365,8 @@ 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);
> @@ -680,6 +682,13 @@ 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;