text: // SPDX-License-Identifier: GPL-2.0-only
  /*
   * Copyright (C) 2011 Google, Inc.
   *
   * Author:
   *	Colin Cross <ccross@android.com>
   */
  
  #include <linux/kernel.h>
  #include <linux/cpu_pm.h>
  #include <linux/module.h>
  #include <linux/notifier.h>
  #include <linux/spinlock.h>
  #include <linux/syscore_ops.h>
  
  static ATOMIC_NOTIFIER_HEAD(cpu_pm_notifier_chain);
  
  static int cpu_pm_notify(enum cpu_pm_event event, int nr_to_call, int *nr_calls)
  {
  	int ret;
  
  	/*
  	 * __atomic_notifier_call_chain has a RCU read critical section, which
  	 * could be disfunctional in cpu idle. Copy RCU_NONIDLE code to let
  	 * RCU know this.
  	 */
  	rcu_irq_enter_irqson();
  	ret = __atomic_notifier_call_chain(&cpu_pm_notifier_chain, event, NULL,
  		nr_to_call, nr_calls);
  	rcu_irq_exit_irqson();
  
  	return notifier_to_errno(ret);
  }
  
  /**
   * cpu_pm_register_notifier - register a driver with cpu_pm
   * @nb: notifier block to register
   *
   * Add a driver to a list of drivers that are notified about
   * CPU and CPU cluster low power entry and exit.
   *
   * This function may sleep, and has the same return conditions as
   * raw_notifier_chain_register.
   */
  int cpu_pm_register_notifier(struct notifier_block *nb)
  {
  	return atomic_notifier_chain_register(&cpu_pm_notifier_chain, nb);
  }
  EXPORT_SYMBOL_GPL(cpu_pm_register_notifier);
  
  /**
   * cpu_pm_unregister_notifier - unregister a driver with cpu_pm
   * @nb: notifier block to be unregistered
   *
   * Remove a driver from the CPU PM notifier list.
   *
   * This function may sleep, and has the same return conditions as
   * raw_notifier_chain_unregister.
   */
  int cpu_pm_unregister_notifier(struct notifier_block *nb)
  {
  	return atomic_notifier_chain_unregister(&cpu_pm_notifier_chain, nb);
  }
  EXPORT_SYMBOL_GPL(cpu_pm_unregister_notifier);
  
  /**
   * cpu_pm_enter - CPU low power entry notifier
   *
   * Notifies listeners that a single CPU is entering a low power state that may
   * cause some blocks in the same power domain as the cpu to reset.
   *
   * Must be called on the affected CPU with interrupts disabled.  Platform is
   * responsible for ensuring that cpu_pm_enter is not called twice on the same
   * CPU before cpu_pm_exit is called. Notified drivers can include VFP
   * co-processor, interrupt controller and its PM extensions, local CPU
   * timers context save/restore which shouldn't be interrupted. Hence it
   * must be called with interrupts disabled.
   *
   * Return conditions are same as __raw_notifier_call_chain.
   */
  int cpu_pm_enter(void)
  {
  	int nr_calls = 0;
  	int ret = 0;
  
  	ret = cpu_pm_notify(CPU_PM_ENTER, -1, &nr_calls);
  	if (ret)
  		/*
  		 * Inform listeners (nr_calls - 1) about failure of CPU PM
  		 * PM entry who are notified earlier to prepare for it.
  		 */
  		cpu_pm_notify(CPU_PM_ENTER_FAILED, nr_calls - 1, NULL);
  
  	return ret;
  }
  EXPORT_SYMBOL_GPL(cpu_pm_enter);
  
  /**
   * cpu_pm_exit - CPU low power exit notifier
   *
   * Notifies listeners that a single CPU is exiting a low power state that may
   * have caused some blocks in the same power domain as the cpu to reset.
   *
   * Notified drivers can include VFP co-processor, interrupt controller
   * and its PM extensions, local CPU timers context save/restore which
   * shouldn't be interrupted. Hence it must be called with interrupts disabled.
   *
   * Return conditions are same as __raw_notifier_call_chain.
   */
  int cpu_pm_exit(void)
  {
  	return cpu_pm_notify(CPU_PM_EXIT, -1, NULL);
  }
  EXPORT_SYMBOL_GPL(cpu_pm_exit);
  
  /**
   * cpu_cluster_pm_enter - CPU cluster low power entry notifier
   *
   * Notifies listeners that all cpus in a power domain are entering a low power
   * state that may cause some blocks in the same power domain to reset.
   *
   * Must be called after cpu_pm_enter has been called on all cpus in the power
   * domain, and before cpu_pm_exit has been called on any cpu in the power
   * domain. Notified drivers can include VFP co-processor, interrupt controller
   * and its PM extensions, local CPU timers context save/restore which
   * shouldn't be interrupted. Hence it must be called with interrupts disabled.
   *
   * Must be called with interrupts disabled.
   *
   * Return conditions are same as __raw_notifier_call_chain.
   */
  int cpu_cluster_pm_enter(void)
  {
  	int nr_calls = 0;
  	int ret = 0;
  
  	ret = cpu_pm_notify(CPU_CLUSTER_PM_ENTER, -1, &nr_calls);
  	if (ret)
  		/*
  		 * Inform listeners (nr_calls - 1) about failure of CPU cluster
  		 * PM entry who are notified earlier to prepare for it.
  		 */
  		cpu_pm_notify(CPU_CLUSTER_PM_ENTER_FAILED, nr_calls - 1, NULL);
  
  	return ret;
  }
  EXPORT_SYMBOL_GPL(cpu_cluster_pm_enter);
  
  /**
   * cpu_cluster_pm_exit - CPU cluster low power exit notifier
   *
   * Notifies listeners that all cpus in a power domain are exiting form a
   * low power state that may have caused some blocks in the same power domain
   * to reset.
   *
   * Must be called after cpu_cluster_pm_enter has been called for the power
   * domain, and before cpu_pm_exit has been called on any cpu in the power
   * domain. Notified drivers can include VFP co-processor, interrupt controller
   * and its PM extensions, local CPU timers context save/restore which
   * shouldn't be interrupted. Hence it must be called with interrupts disabled.
   *
   * Return conditions are same as __raw_notifier_call_chain.
   */
  int cpu_cluster_pm_exit(void)
  {
  	return cpu_pm_notify(CPU_CLUSTER_PM_EXIT, -1, NULL);
  }
  EXPORT_SYMBOL_GPL(cpu_cluster_pm_exit);
  
  #ifdef CONFIG_PM
  static int cpu_pm_suspend(void)
  {
  	int ret;
  
  	ret = cpu_pm_enter();
  	if (ret)
  		return ret;
  
  	ret = cpu_cluster_pm_enter();
  	return ret;
  }
  
  static void cpu_pm_resume(void)
  {
  	cpu_cluster_pm_exit();
  	cpu_pm_exit();
  }
  
  static struct syscore_ops cpu_pm_syscore_ops = {
  	.suspend = cpu_pm_suspend,
  	.resume = cpu_pm_resume,
  };
  
  static int cpu_pm_init(void)
  {
  	register_syscore_ops(&cpu_pm_syscore_ops);
  	return 0;
  }
  core_initcall(cpu_pm_init);
  #endif
  