[PATCH v2 1/1] cpuidle: sysfs: Display idle state enter function name

[Aaron Tomlin <atomlin@atomlin.com>]

This patch introduces a read-only "enter_function" attribute to the
cpuidle sysfs interface. It exports the kernel symbolic name of the
enter callback responsible for executing the CPU idle state entry
state->enter(). It allows users to reliably map an abstract C-state
e.g., "C0", to its concrete kernel implementation (e.g., poll_idle).

Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
 Documentation/ABI/testing/sysfs-devices-system-cpu | 7 +++++++
 drivers/cpuidle/sysfs.c                            | 9 +++++++++
 2 files changed, 16 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index 8aed6d94c4cd..7be4555d502a 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -217,6 +217,13 @@ Description:
 		time (in microseconds) this cpu should spend in this idle state
 		to make the transition worth the effort.
 
+What:		/sys/devices/system/cpu/cpuX/cpuidle/state<N>/enter_function
+Date:		November 2025
+KernelVersion:	v6.18
+Contact:	Linux power management list <linux-pm@vger.kernel.org>
+Description:
+		(RO) Display the symbolic name of the idle state's enter callback.
+
 What:		/sys/devices/system/cpu/cpuX/cpuidle/state<N>/s2idle/
 Date:		March 2018
 KernelVersion:	v4.17
diff --git a/drivers/cpuidle/sysfs.c b/drivers/cpuidle/sysfs.c
index 61de64817604..dbd8d796ad29 100644
--- a/drivers/cpuidle/sysfs.c
+++ b/drivers/cpuidle/sysfs.c
@@ -314,6 +314,13 @@ static ssize_t show_state_default_status(struct cpuidle_state *state,
 		       state->flags & CPUIDLE_FLAG_OFF ? "disabled" : "enabled");
 }
 
+static ssize_t show_state_enter_function(struct cpuidle_state *state,
+					 struct cpuidle_state_usage *state_usage,
+					 char *buf)
+{
+	return sysfs_emit(buf, "%ps\n", state->enter);
+}
+
 define_one_state_ro(name, show_state_name);
 define_one_state_ro(desc, show_state_desc);
 define_one_state_ro(latency, show_state_exit_latency);
@@ -326,6 +333,7 @@ define_one_state_rw(disable, show_state_disable, store_state_disable);
 define_one_state_ro(above, show_state_above);
 define_one_state_ro(below, show_state_below);
 define_one_state_ro(default_status, show_state_default_status);
+define_one_state_ro(enter_function, show_state_enter_function);
 
 static struct attribute *cpuidle_state_default_attrs[] = {
 	&attr_name.attr,
@@ -340,6 +348,7 @@ static struct attribute *cpuidle_state_default_attrs[] = {
 	&attr_above.attr,
 	&attr_below.attr,
 	&attr_default_status.attr,
+	&attr_enter_function.attr,
 	NULL
 };
 ATTRIBUTE_GROUPS(cpuidle_state_default);
-- 
2.51.0