/*
   * linux/kernel/time/tick-common.c
   *
   * This file contains the base functions to manage periodic tick
   * related events.
   *
   * Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
   * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
   * Copyright(C) 2006-2007, Timesys Corp., Thomas Gleixner
   *
   * This code is licenced under the GPL version 2. For details see
   * kernel-base/COPYING.
   */
  #include <linux/cpu.h>
  #include <linux/err.h>
  #include <linux/hrtimer.h>

  #include <linux/interrupt.h>

  #include <linux/percpu.h>
  #include <linux/profile.h>
  #include <linux/sched.h>

  #include <linux/module.h>

  #include <asm/irq_regs.h>

  #include "tick-internal.h"

  /*
   * Tick devices
   */

  DEFINE_PER_CPU(struct tick_device, tick_cpu_device);

  /*
   * Tick next event: keeps track of the tick time
   */

  ktime_t tick_next_period;
  ktime_t tick_period;

  
  /*
   * tick_do_timer_cpu is a timer core internal variable which holds the CPU NR
   * which is responsible for calling do_timer(), i.e. the timekeeping stuff. This
   * variable has two functions:
   *
   * 1) Prevent a thundering herd issue of a gazillion of CPUs trying to grab the
   *    timekeeping lock all at once. Only the CPU which is assigned to do the
   *    update is handling it.
   *
   * 2) Hand off the duty in the NOHZ idle case by setting the value to
   *    TICK_DO_TIMER_NONE, i.e. a non existing CPU. So the next cpu which looks
   *    at it will take over and keep the time keeping alive.  The handover
   *    procedure also covers cpu hotplug.
   */

  int tick_do_timer_cpu __read_mostly = TICK_DO_TIMER_BOOT;

  /*
   * Debugging: see timer_list.c
   */
  struct tick_device *tick_get_device(int cpu)
  {
  	return &per_cpu(tick_cpu_device, cpu);
  }

  /**
   * tick_is_oneshot_available - check for a oneshot capable event device
   */
  int tick_is_oneshot_available(void)
  {

  	struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);

  	if (!dev || !(dev->features & CLOCK_EVT_FEAT_ONESHOT))
  		return 0;
  	if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))
  		return 1;
  	return tick_broadcast_oneshot_available();

  }

  /*
   * Periodic tick
   */
  static void tick_periodic(int cpu)
  {
  	if (tick_do_timer_cpu == cpu) {

  		write_seqlock(&jiffies_lock);

  
  		/* Keep track of the next tick event */
  		tick_next_period = ktime_add(tick_next_period, tick_period);
  
  		do_timer(1);

  		write_sequnlock(&jiffies_lock);

  		update_wall_time();

  	}
  
  	update_process_times(user_mode(get_irq_regs()));
  	profile_tick(CPU_PROFILING);
  }
  
  /*
   * Event handler for periodic ticks
   */
  void tick_handle_periodic(struct clock_event_device *dev)
  {
  	int cpu = smp_processor_id();

  	ktime_t next = dev->next_event;

  
  	tick_periodic(cpu);
  
  	if (dev->mode != CLOCK_EVT_MODE_ONESHOT)
  		return;

  	for (;;) {

  		/*
  		 * Setup the next period for devices, which do not have
  		 * periodic mode:
  		 */
  		next = ktime_add(next, tick_period);

  		if (!clockevents_program_event(dev, next, false))

  			return;

  		/*
  		 * Have to be careful here. If we're in oneshot mode,
  		 * before we call tick_periodic() in a loop, we need
  		 * to be sure we're using a real hardware clocksource.
  		 * Otherwise we could get trapped in an infinite
  		 * loop, as the tick_periodic() increments jiffies,

  		 * which then will increment time, possibly causing

  		 * the loop to trigger again and again.
  		 */
  		if (timekeeping_valid_for_hres())
  			tick_periodic(cpu);

  	}
  }
  
  /*
   * Setup the device for a periodic tick
   */

  void tick_setup_periodic(struct clock_event_device *dev, int broadcast)

  {

  	tick_set_periodic_handler(dev, broadcast);
  
  	/* Broadcast setup ? */
  	if (!tick_device_is_functional(dev))
  		return;

  	if ((dev->features & CLOCK_EVT_FEAT_PERIODIC) &&
  	    !tick_broadcast_oneshot_active()) {

  		clockevents_set_mode(dev, CLOCK_EVT_MODE_PERIODIC);
  	} else {
  		unsigned long seq;
  		ktime_t next;
  
  		do {

  			seq = read_seqbegin(&jiffies_lock);

  			next = tick_next_period;

  		} while (read_seqretry(&jiffies_lock, seq));

  
  		clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);
  
  		for (;;) {

  			if (!clockevents_program_event(dev, next, false))

  				return;
  			next = ktime_add(next, tick_period);
  		}
  	}
  }
  
  /*
   * Setup the tick device
   */
  static void tick_setup_device(struct tick_device *td,
  			      struct clock_event_device *newdev, int cpu,

  			      const struct cpumask *cpumask)

  {
  	ktime_t next_event;
  	void (*handler)(struct clock_event_device *) = NULL;
  
  	/*
  	 * First device setup ?
  	 */
  	if (!td->evtdev) {
  		/*
  		 * If no cpu took the do_timer update, assign it to
  		 * this cpu:
  		 */

  		if (tick_do_timer_cpu == TICK_DO_TIMER_BOOT) {

  			if (!tick_nohz_full_cpu(cpu))

  				tick_do_timer_cpu = cpu;
  			else
  				tick_do_timer_cpu = TICK_DO_TIMER_NONE;

  			tick_next_period = ktime_get();
  			tick_period = ktime_set(0, NSEC_PER_SEC / HZ);
  		}
  
  		/*
  		 * Startup in periodic mode first.
  		 */
  		td->mode = TICKDEV_MODE_PERIODIC;
  	} else {
  		handler = td->evtdev->event_handler;
  		next_event = td->evtdev->next_event;

  		td->evtdev->event_handler = clockevents_handle_noop;

  	}
  
  	td->evtdev = newdev;
  
  	/*
  	 * When the device is not per cpu, pin the interrupt to the
  	 * current cpu:
  	 */

  	if (!cpumask_equal(newdev->cpumask, cpumask))

  		irq_set_affinity(newdev->irq, cpumask);

  	/*
  	 * When global broadcasting is active, check if the current
  	 * device is registered as a placeholder for broadcast mode.
  	 * This allows us to handle this x86 misfeature in a generic

  	 * way. This function also returns !=0 when we keep the
  	 * current active broadcast state for this CPU.

  	 */
  	if (tick_device_uses_broadcast(newdev, cpu))
  		return;

  	if (td->mode == TICKDEV_MODE_PERIODIC)
  		tick_setup_periodic(newdev, 0);

  	else
  		tick_setup_oneshot(newdev, handler, next_event);

  }

  void tick_install_replacement(struct clock_event_device *newdev)
  {

  	struct tick_device *td = this_cpu_ptr(&tick_cpu_device);

  	int cpu = smp_processor_id();
  
  	clockevents_exchange_device(td->evtdev, newdev);
  	tick_setup_device(td, newdev, cpu, cpumask_of(cpu));
  	if (newdev->features & CLOCK_EVT_FEAT_ONESHOT)
  		tick_oneshot_notify();
  }

  static bool tick_check_percpu(struct clock_event_device *curdev,
  			      struct clock_event_device *newdev, int cpu)
  {
  	if (!cpumask_test_cpu(cpu, newdev->cpumask))
  		return false;
  	if (cpumask_equal(newdev->cpumask, cpumask_of(cpu)))
  		return true;
  	/* Check if irq affinity can be set */
  	if (newdev->irq >= 0 && !irq_can_set_affinity(newdev->irq))
  		return false;
  	/* Prefer an existing cpu local device */
  	if (curdev && cpumask_equal(curdev->cpumask, cpumask_of(cpu)))
  		return false;
  	return true;
  }
  
  static bool tick_check_preferred(struct clock_event_device *curdev,
  				 struct clock_event_device *newdev)
  {
  	/* Prefer oneshot capable device */
  	if (!(newdev->features & CLOCK_EVT_FEAT_ONESHOT)) {
  		if (curdev && (curdev->features & CLOCK_EVT_FEAT_ONESHOT))
  			return false;
  		if (tick_oneshot_mode_active())
  			return false;
  	}

  	/*
  	 * Use the higher rated one, but prefer a CPU local device with a lower
  	 * rating than a non-CPU local device
  	 */
  	return !curdev ||
  		newdev->rating > curdev->rating ||
  	       !cpumask_equal(curdev->cpumask, newdev->cpumask);

  }

  /*

   * Check whether the new device is a better fit than curdev. curdev
   * can be NULL !
   */
  bool tick_check_replacement(struct clock_event_device *curdev,
  			    struct clock_event_device *newdev)
  {

  	if (!tick_check_percpu(curdev, newdev, smp_processor_id()))

  		return false;
  
  	return tick_check_preferred(curdev, newdev);
  }
  
  /*

   * Check, if the new registered device should be used. Called with
   * clockevents_lock held and interrupts disabled.

   */

  void tick_check_new_device(struct clock_event_device *newdev)

  {
  	struct clock_event_device *curdev;
  	struct tick_device *td;

  	int cpu;

  
  	cpu = smp_processor_id();

  	if (!cpumask_test_cpu(cpu, newdev->cpumask))

  		goto out_bc;

  
  	td = &per_cpu(tick_cpu_device, cpu);
  	curdev = td->evtdev;

  
  	/* cpu local device ? */

  	if (!tick_check_percpu(curdev, newdev, cpu))
  		goto out_bc;

  	/* Preference decision */
  	if (!tick_check_preferred(curdev, newdev))
  		goto out_bc;

  	if (!try_module_get(newdev->owner))
  		return;

  	/*
  	 * Replace the eventually existing device by the new

  	 * device. If the current device is the broadcast device, do
  	 * not give it back to the clockevents layer !

  	 */

  	if (tick_is_broadcast_device(curdev)) {

  		clockevents_shutdown(curdev);

  		curdev = NULL;
  	}

  	clockevents_exchange_device(curdev, newdev);

  	tick_setup_device(td, newdev, cpu, cpumask_of(cpu));

  	if (newdev->features & CLOCK_EVT_FEAT_ONESHOT)
  		tick_oneshot_notify();

  	return;

  
  out_bc:
  	/*
  	 * Can the new device be used as a broadcast device ?
  	 */

  	tick_install_broadcast_device(newdev);

  }
  
  /*

   * Transfer the do_timer job away from a dying cpu.
   *
   * Called with interrupts disabled.
   */

  void tick_handover_do_timer(int *cpup)

  {
  	if (*cpup == tick_do_timer_cpu) {
  		int cpu = cpumask_first(cpu_online_mask);
  
  		tick_do_timer_cpu = (cpu < nr_cpu_ids) ? cpu :
  			TICK_DO_TIMER_NONE;
  	}
  }
  
  /*

   * Shutdown an event device on a given cpu:
   *
   * This is called on a life CPU, when a CPU is dead. So we cannot
   * access the hardware device itself.
   * We just set the mode and remove it from the lists.
   */

  void tick_shutdown(unsigned int *cpup)

  {
  	struct tick_device *td = &per_cpu(tick_cpu_device, *cpup);
  	struct clock_event_device *dev = td->evtdev;

  	td->mode = TICKDEV_MODE_PERIODIC;
  	if (dev) {
  		/*
  		 * Prevent that the clock events layer tries to call
  		 * the set mode function!
  		 */
  		dev->mode = CLOCK_EVT_MODE_UNUSED;
  		clockevents_exchange_device(dev, NULL);

  		dev->event_handler = clockevents_handle_noop;

  		td->evtdev = NULL;
  	}

  }

  void tick_suspend(void)

  {

  	struct tick_device *td = this_cpu_ptr(&tick_cpu_device);

  	clockevents_shutdown(td->evtdev);

  }

  void tick_resume(void)

  {

  	struct tick_device *td = this_cpu_ptr(&tick_cpu_device);

  	int broadcast = tick_resume_broadcast();

  	clockevents_set_mode(td->evtdev, CLOCK_EVT_MODE_RESUME);
  
  	if (!broadcast) {
  		if (td->mode == TICKDEV_MODE_PERIODIC)
  			tick_setup_periodic(td->evtdev, 0);
  		else
  			tick_resume_oneshot();
  	}

  }

  /**
   * tick_init - initialize the tick control

   */
  void __init tick_init(void)
  {

  	tick_broadcast_init();

  	tick_nohz_init();

  }