/*
   * Generic entry point for the idle threads
   */
  #include <linux/sched.h>
  #include <linux/cpu.h>
  #include <linux/cpuidle.h>
  #include <linux/tick.h>
  #include <linux/mm.h>
  #include <linux/stackprotector.h>

  #include <linux/suspend.h>

  
  #include <asm/tlb.h>
  
  #include <trace/events/power.h>

  #include "sched.h"

  static int __read_mostly cpu_idle_force_poll;
  
  void cpu_idle_poll_ctrl(bool enable)
  {
  	if (enable) {
  		cpu_idle_force_poll++;
  	} else {
  		cpu_idle_force_poll--;
  		WARN_ON_ONCE(cpu_idle_force_poll < 0);
  	}
  }
  
  #ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
  static int __init cpu_idle_poll_setup(char *__unused)
  {
  	cpu_idle_force_poll = 1;
  	return 1;
  }
  __setup("nohlt", cpu_idle_poll_setup);
  
  static int __init cpu_idle_nopoll_setup(char *__unused)
  {
  	cpu_idle_force_poll = 0;
  	return 1;
  }
  __setup("hlt", cpu_idle_nopoll_setup);
  #endif
  
  static inline int cpu_idle_poll(void)
  {
  	rcu_idle_enter();
  	trace_cpu_idle_rcuidle(0, smp_processor_id());
  	local_irq_enable();

  	while (!tif_need_resched() &&
  		(cpu_idle_force_poll || tick_check_broadcast_expired()))

  		cpu_relax();
  	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
  	rcu_idle_exit();
  	return 1;
  }
  
  /* Weak implementations for optional arch specific functions */
  void __weak arch_cpu_idle_prepare(void) { }
  void __weak arch_cpu_idle_enter(void) { }
  void __weak arch_cpu_idle_exit(void) { }
  void __weak arch_cpu_idle_dead(void) { }
  void __weak arch_cpu_idle(void)
  {
  	cpu_idle_force_poll = 1;
  	local_irq_enable();
  }

  /**
   * cpuidle_idle_call - the main idle function
   *
   * NOTE: no locks or semaphores should be used here

   *
   * On archs that support TIF_POLLING_NRFLAG, is called with polling
   * set, and it returns with polling set.  If it ever stops polling, it
   * must clear the polling bit.

   */

  static void cpuidle_idle_call(void)

  {
  	struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
  	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);

  	int next_state, entered_state;

  	bool reflect;

  	/*
  	 * Check if the idle task must be rescheduled. If it is the

  	 * case, exit the function after re-enabling the local irq.

  	 */

  	if (need_resched()) {

  		local_irq_enable();

  		return;

  	}

  	/*
  	 * During the idle period, stop measuring the disabled irqs
  	 * critical sections latencies
  	 */

  	stop_critical_timings();

  
  	/*
  	 * Tell the RCU framework we are entering an idle section,
  	 * so no more rcu read side critical sections and one more
  	 * step to the grace period
  	 */

  	rcu_idle_enter();

  	if (cpuidle_not_available(drv, dev))
  		goto use_default;

  	/*

  	 * Suspend-to-idle ("freeze") is a system state in which all user space
  	 * has been frozen, all I/O devices have been suspended and the only
  	 * activity happens here and in iterrupts (if any).  In that case bypass
  	 * the cpuidle governor and go stratight for the deepest idle state
  	 * available.  Possibly also suspend the local tick and the entire
  	 * timekeeping to prevent timer interrupts from kicking us out of idle
  	 * until a proper wakeup interrupt happens.
  	 */
  	if (idle_should_freeze()) {

  		entered_state = cpuidle_enter_freeze(drv, dev);
  		if (entered_state >= 0) {
  			local_irq_enable();
  			goto exit_idle;
  		}
  
  		reflect = false;
  		next_state = cpuidle_find_deepest_state(drv, dev);
  	} else {
  		reflect = true;
  		/*
  		 * Ask the cpuidle framework to choose a convenient idle state.
  		 */
  		next_state = cpuidle_select(drv, dev);

  	}

  	/* Fall back to the default arch idle method on errors. */

  	if (next_state < 0)
  		goto use_default;

  
  	/*
  	 * The idle task must be scheduled, it is pointless to
  	 * go to idle, just update no idle residency and get
  	 * out of this function
  	 */
  	if (current_clr_polling_and_test()) {
  		dev->last_residency = 0;
  		entered_state = next_state;
  		local_irq_enable();
  		goto exit_idle;

  	}

  	/* Take note of the planned idle state. */
  	idle_set_state(this_rq(), &drv->states[next_state]);

  	/*
  	 * Enter the idle state previously returned by the governor decision.
  	 * This function will block until an interrupt occurs and will take
  	 * care of re-enabling the local interrupts
  	 */
  	entered_state = cpuidle_enter(drv, dev, next_state);

  	/* The cpu is no longer idle or about to enter idle. */
  	idle_set_state(this_rq(), NULL);

  	if (entered_state == -EBUSY)
  		goto use_default;

  
  	/*
  	 * Give the governor an opportunity to reflect on the outcome
  	 */

  	if (reflect)
  		cpuidle_reflect(dev, entered_state);

  
  exit_idle:

  	__current_set_polling();

  	/*

  	 * It is up to the idle functions to reenable local interrupts

  	 */

  	if (WARN_ON_ONCE(irqs_disabled()))
  		local_irq_enable();
  
  	rcu_idle_exit();
  	start_critical_timings();

  	return;
  
  use_default:
  	/*
  	 * We can't use the cpuidle framework, let's use the default
  	 * idle routine.
  	 */
  	if (current_clr_polling_and_test())
  		local_irq_enable();
  	else
  		arch_cpu_idle();
  
  	goto exit_idle;

  }

  DEFINE_PER_CPU(bool, cpu_dead_idle);

  /*
   * Generic idle loop implementation

   *
   * Called with polling cleared.

   */
  static void cpu_idle_loop(void)
  {
  	while (1) {

  		/*
  		 * If the arch has a polling bit, we maintain an invariant:
  		 *
  		 * Our polling bit is clear if we're not scheduled (i.e. if
  		 * rq->curr != rq->idle).  This means that, if rq->idle has
  		 * the polling bit set, then setting need_resched is
  		 * guaranteed to cause the cpu to reschedule.
  		 */
  
  		__current_set_polling();

  		tick_nohz_idle_enter();
  
  		while (!need_resched()) {
  			check_pgt_cache();
  			rmb();

  			if (cpu_is_offline(smp_processor_id())) {

  				rcu_cpu_notify(NULL, CPU_DYING_IDLE,
  					       (void *)(long)smp_processor_id());

  				smp_mb(); /* all activity before dead. */
  				this_cpu_write(cpu_dead_idle, true);

  				arch_cpu_idle_dead();

  			}

  
  			local_irq_disable();
  			arch_cpu_idle_enter();
  
  			/*
  			 * In poll mode we reenable interrupts and spin.
  			 *
  			 * Also if we detected in the wakeup from idle
  			 * path that the tick broadcast device expired
  			 * for us, we don't want to go deep idle as we
  			 * know that the IPI is going to arrive right
  			 * away
  			 */

  			if (cpu_idle_force_poll || tick_check_broadcast_expired())

  				cpu_idle_poll();

  			else
  				cpuidle_idle_call();

  			arch_cpu_idle_exit();

  		}

  
  		/*
  		 * Since we fell out of the loop above, we know
  		 * TIF_NEED_RESCHED must be set, propagate it into
  		 * PREEMPT_NEED_RESCHED.
  		 *
  		 * This is required because for polling idle loops we will
  		 * not have had an IPI to fold the state for us.
  		 */
  		preempt_set_need_resched();

  		tick_nohz_idle_exit();

  		__current_clr_polling();
  
  		/*

  		 * We promise to call sched_ttwu_pending and reschedule
  		 * if need_resched is set while polling is set.  That
  		 * means that clearing polling needs to be visible
  		 * before doing these things.

  		 */
  		smp_mb__after_atomic();

  		sched_ttwu_pending();

  		schedule_preempt_disabled();
  	}
  }
  
  void cpu_startup_entry(enum cpuhp_state state)
  {
  	/*
  	 * This #ifdef needs to die, but it's too late in the cycle to
  	 * make this generic (arm and sh have never invoked the canary
  	 * init for the non boot cpus!). Will be fixed in 3.11
  	 */
  #ifdef CONFIG_X86
  	/*
  	 * If we're the non-boot CPU, nothing set the stack canary up
  	 * for us. The boot CPU already has it initialized but no harm
  	 * in doing it again. This is a good place for updating it, as
  	 * we wont ever return from this function (so the invalid
  	 * canaries already on the stack wont ever trigger).
  	 */
  	boot_init_stack_canary();
  #endif

  	arch_cpu_idle_prepare();
  	cpu_idle_loop();
  }