Revert the ACPI idle driver registration lifecycle introduced by upstream
commit 13ebeef6a1b9 ("ACPI: processor: idle: Optimize ACPI idle driver
registration").

That change moved ACPI idle driver registration out of
acpi_processor_power_init() and ahead of driver_register(). This breaks the
established lifecycle on Xen dom0, where cpuidle is disabled during early
architecture setup. Restore the 6.18.51 per-processor registration behavior.

Keep unrelated 6.18.52 fixes, notably _LPI bounds validation and cpufreq
notifier cleanup on initialization failure.

diff --git a/drivers/acpi/processor_driver.c b/drivers/acpi/processor_driver.c
index 06589bf48..174dfb0ac 100644
--- a/drivers/acpi/processor_driver.c
+++ b/drivers/acpi/processor_driver.c
@@ -259,11 +259,9 @@ static int __init acpi_processor_driver_init(void)
 		acpi_processor_ignore_ppc_init();
 	}
 
-	acpi_processor_register_idle_driver();
-
 	result = driver_register(&acpi_processor_driver);
 	if (result < 0)
-		goto unregister_idle_drv;
+		goto unregister_cpufreq;
 
 	result = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
 				   "acpi/cpu-drv:online",
@@ -289,9 +287,7 @@ static int __init acpi_processor_driver_init(void)
 err:
 	driver_unregister(&acpi_processor_driver);
 
-unregister_idle_drv:
-	acpi_processor_unregister_idle_driver();
-
+unregister_cpufreq:
 	if (acpi_processor_cpufreq_init) {
 		cpufreq_unregister_notifier(&acpi_processor_notifier_block,
 					    CPUFREQ_POLICY_NOTIFIER);
@@ -315,7 +311,6 @@ static void __exit acpi_processor_driver_exit(void)
 	cpuhp_remove_state_nocalls(hp_online);
 	cpuhp_remove_state_nocalls(CPUHP_ACPI_CPUDRV_DEAD);
 	driver_unregister(&acpi_processor_driver);
-	acpi_processor_unregister_idle_driver();
 }
 
 module_init(acpi_processor_driver_init);
diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index 5c6f736ba..7b4e948fa 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -831,13 +831,19 @@ static int acpi_processor_setup_cstates(struct acpi_processor *pr)
 	return 0;
 }
 
-static inline void acpi_processor_update_max_cstate(void)
+static inline void acpi_processor_cstate_first_run_checks(void)
 {
+	static int first_run;
+
+	if (first_run)
+		return;
 	dmi_check_system(processor_power_dmi_table);
 	max_cstate = acpi_processor_cstate_check(max_cstate);
 	if (max_cstate < ACPI_C_STATES_MAX)
 		pr_notice("processor limited to max C-state %d\n", max_cstate);
 
+	first_run++;
+
 	if (nocst)
 		return;
 
@@ -846,7 +852,7 @@ static inline void acpi_processor_update_max_cstate(void)
 #else
 
 static inline int disabled_by_idle_boot_param(void) { return 0; }
-static inline void acpi_processor_update_max_cstate(void) { }
+static inline void acpi_processor_cstate_first_run_checks(void) { }
 static int acpi_processor_get_cstate_info(struct acpi_processor *pr)
 {
 	return -ENODEV;
@@ -1365,59 +1371,7 @@ int acpi_processor_power_state_has_changed(struct acpi_processor *pr)
 	return 0;
 }
 
-void acpi_processor_register_idle_driver(void)
-{
-	struct acpi_processor *pr;
-	int ret = -ENODEV;
-	int cpu;
-
-	/*
-	 * If a cpuidle driver is already registered, there is no need to
-	 * evaluate _CST or attempt to register the ACPI idle driver.
-	 */
-	if (cpuidle_get_driver()) {
-		pr_debug("cpuidle driver %pS already registered.\n", cpuidle_get_driver());
-		return;
-	}
-
-	acpi_processor_update_max_cstate();
-
-	/*
-	 * ACPI idle driver is used by all possible CPUs.
-	 * Use the processor power info of one in them to set up idle states.
-	 * Note that the existing idle handler will be used on platforms that
-	 * only support C1.
-	 */
-	for_each_possible_cpu(cpu) {
-		pr = per_cpu(processors, cpu);
-		if (!pr)
-			continue;
-
-		ret = acpi_processor_get_power_info(pr);
-		if (!ret) {
-			pr->flags.power_setup_done = 1;
-			acpi_processor_setup_cpuidle_states(pr);
-			break;
-		}
-	}
-
-	if (ret) {
-		pr_debug("No ACPI power information from any CPUs.\n");
-		return;
-	}
-
-	ret = cpuidle_register_driver(&acpi_idle_driver);
-	if (ret) {
-		pr_debug("register %s failed.\n", acpi_idle_driver.name);
-		return;
-	}
-	pr_debug("%s registered with cpuidle.\n", acpi_idle_driver.name);
-}
-
-void acpi_processor_unregister_idle_driver(void)
-{
-	cpuidle_unregister_driver(&acpi_idle_driver);
-}
+static int acpi_processor_registered;
 
 int acpi_processor_power_init(struct acpi_processor *pr)
 {
@@ -1427,10 +1381,27 @@ int acpi_processor_power_init(struct acpi_processor *pr)
 	if (disabled_by_idle_boot_param())
 		return 0;
 
+	acpi_processor_cstate_first_run_checks();
+
 	if (!acpi_processor_get_power_info(pr))
 		pr->flags.power_setup_done = 1;
 
+	/*
+	 * Install the idle handler if processor power management is supported.
+	 * Note that the existing idle handler is used on platforms that only
+	 * support C1.
+	 */
 	if (pr->flags.power) {
+		/* Register acpi_idle_driver if not already registered */
+		if (!acpi_processor_registered) {
+			acpi_processor_setup_cpuidle_states(pr);
+			retval = cpuidle_register_driver(&acpi_idle_driver);
+			if (retval)
+				return retval;
+			pr_debug("%s registered with cpuidle\n",
+				 acpi_idle_driver.name);
+		}
+
 		dev = kzalloc(sizeof(*dev), GFP_KERNEL);
 		if (!dev)
 			return -ENOMEM;
@@ -1443,11 +1414,14 @@ int acpi_processor_power_init(struct acpi_processor *pr)
 		 */
 		retval = cpuidle_register_device(dev);
 		if (retval) {
+			if (acpi_processor_registered == 0)
+				cpuidle_unregister_driver(&acpi_idle_driver);
 
 			per_cpu(acpi_cpuidle_device, pr->id) = NULL;
 			kfree(dev);
 			return retval;
 		}
+		acpi_processor_registered++;
 	}
 	return 0;
 }
@@ -1461,6 +1435,10 @@ int acpi_processor_power_exit(struct acpi_processor *pr)
 
 	if (pr->flags.power) {
 		cpuidle_unregister_device(dev);
+		acpi_processor_registered--;
+		if (acpi_processor_registered == 0)
+			cpuidle_unregister_driver(&acpi_idle_driver);
+
 		kfree(dev);
 	}
 
diff --git a/include/acpi/processor.h b/include/acpi/processor.h
index ff864c1ce..d0eccbd92 100644
--- a/include/acpi/processor.h
+++ b/include/acpi/processor.h
@@ -423,8 +423,6 @@ int acpi_processor_power_init(struct acpi_processor *pr);
 int acpi_processor_power_exit(struct acpi_processor *pr);
 int acpi_processor_power_state_has_changed(struct acpi_processor *pr);
 int acpi_processor_hotplug(struct acpi_processor *pr);
-void acpi_processor_register_idle_driver(void);
-void acpi_processor_unregister_idle_driver(void);
 #else
 static inline int acpi_processor_power_init(struct acpi_processor *pr)
 {