linux-kernel - [PATCH v2 1/6] of: add infra for finding CPU id from phandle

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Message-ID: <20250502161300.1411-2-alireza.sanaee@huawei.com>
Date: Fri, 2 May 2025 17:12:55 +0100
From: Alireza Sanaee <alireza.sanaee@...wei.com>
To: <devicetree@...r.kernel.org>
CC: <robh@...nel.org>, <jonathan.cameron@...wei.com>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
	<linuxarm@...wei.com>, <mark.rutland@....com>,
	<shameerali.kolothum.thodi@...wei.com>
Subject: [PATCH v2 1/6] of: add infra for finding CPU id from phandle

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.
---
 drivers/of/cpu.c   | 24 ++++++++++++++++++++++++
 include/linux/of.h |  8 ++++++++
 2 files changed, 32 insertions(+)

diff --git a/drivers/of/cpu.c b/drivers/of/cpu.c
index 5214dc3d05ae..1e8d1fa04d3c 100644
--- a/drivers/of/cpu.c
+++ b/drivers/of/cpu.c
@@ -173,6 +173,30 @@ 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.
+ *
+ * Return: The logical CPU number of the given CPU device_node or -ENODEV if
+ * the CPU is not found. If the property is not found, it returns -1. On
+ * success, cpu_np will always point to the retrieved CPU device_node.
+ */
+int of_cpu_phandle_to_id(const struct device_node *node,
+			 struct device_node **cpu_np)
+{
+	if (!node)
+		return -1;
+
+	*cpu_np = of_parse_phandle(node, "cpu", 0);
+	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..4087f516b3db 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);
 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 +664,12 @@ 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)
+{
+	return -ENODEV;
+}
+
 static inline struct device_node *of_get_next_cpu_node(struct device_node *prev)
 {
 	return NULL;
-- 
2.34.1