[PATCH v2 2/2] ACPI: processor: idle: Fix incorrect power management decisions after power notify

[Huisong Li]

When a power notification event occurs, existing ACPI idle states may
become obsolete. The current implementation only performs a partial
update, leaving critical cpuidle parameters—such as target_residency_ns
and exit_latency_ns—stale. Furthermore, per-CPU cpuidle_device data,
including last_residency_ns, states_usage, and the disable flag, are not
properly synchronized. Using these stale values leads to incorrect power
management decisions.

To ensure all parameters are correctly synchronized, modify the
notification handling logic:
1. Unregister all cpuidle_device instances to ensure a clean slate.
2. Unregister and re-register the ACPI idle driver. This forces the
   framework to re-evaluate global state parameters and ensures the
   driver state matches the new hardware power profile.
3. Re-initialize power information and re-register cpuidle_device for
   all possible CPUs to restore functional idle management.

This complete reset ensures that the cpuidle framework and the underlying
ACPI states are perfectly synchronized after a power state change.

Signed-off-by: Huisong Li <lihuisong@xxxxxxxxxx>
---
 drivers/acpi/processor_idle.c | 45 +++++++++++++++++++----------------
 1 file changed, 25 insertions(+), 20 deletions(-)

diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index 479995a4c48a..f0054b2b20c1 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -1308,37 +1308,42 @@ int acpi_processor_power_state_has_changed(struct acpi_processor *pr)
 	 */
 
 	if (pr->id == 0 && cpuidle_get_driver() == &acpi_idle_driver) {
-
 		/* Protect against cpu-hotplug */
 		cpus_read_lock();
-		cpuidle_pause_and_lock();
 
-		/* Disable all cpuidle devices */
-		for_each_online_cpu(cpu) {
+		/* Unregister cpuidle device of all CPUs */
+		cpuidle_pause_and_lock();
+		for_each_possible_cpu(cpu) {
+			dev = per_cpu(acpi_cpuidle_device, cpu);
 			_pr = per_cpu(processors, cpu);
-			if (!_pr || !_pr->flags.power_setup_done)
+			if (!_pr || !_pr->flags.power || !dev)
 				continue;
-			dev = per_cpu(acpi_cpuidle_device, cpu);
-			cpuidle_disable_device(dev);
+
+			cpuidle_unregister_device_no_lock(dev);
+			kfree(dev);
+			_pr->flags.power = 0;
 		}
+		cpuidle_resume_and_unlock();
 
-		/* Populate Updated C-state information */
-		acpi_processor_get_power_info(pr);
-		acpi_processor_setup_cpuidle_states(pr);
+		/*
+		 * Unregister ACPI idle driver, reinitialize ACPI idle states
+		 * and register ACPI idle driver again.
+		 */
+		acpi_processor_unregister_idle_driver();
+		acpi_processor_register_idle_driver();
 
-		/* Enable all cpuidle devices */
-		for_each_online_cpu(cpu) {
+		/*
+		 * Reinitialize power information of all CPUs and re-register
+		 * all cpuidle devices. Now idle states is ok to use, can enable
+		 * cpuidle of each CPU safely one by one.
+		 */
+		for_each_possible_cpu(cpu) {
 			_pr = per_cpu(processors, cpu);
-			if (!_pr || !_pr->flags.power_setup_done)
+			if (!_pr)
 				continue;
-			acpi_processor_get_power_info(_pr);
-			if (_pr->flags.power) {
-				dev = per_cpu(acpi_cpuidle_device, cpu);
-				acpi_processor_setup_cpuidle_dev(_pr, dev);
-				cpuidle_enable_device(dev);
-			}
+			acpi_processor_power_init(_pr);
 		}
-		cpuidle_resume_and_unlock();
+
 		cpus_read_unlock();
 	}
 
-- 
2.33.0