/**
 * struct clock_event_device - clock event device descriptor
 * @event_handler:	Assigned by the framework to be called by the low
 *			level handler of the event source
 * @set_next_event:	set next event function using a clocksource delta
 * @set_next_ktime:	set next event function using a direct ktime value
 * @next_event:		local storage for the next event in oneshot mode
 * @max_delta_ns:	maximum delta value in ns
 * @min_delta_ns:	minimum delta value in ns
 * @mult:		nanosecond to cycles multiplier
 * @shift:		nanoseconds to cycles divisor (power of two)
 * @mode:		operating mode assigned by the management code
 * @features:		features
 * @retries:		number of forced programming retries
 * @set_mode:		set mode function
 * @broadcast:		function to broadcast events
 * @min_delta_ticks:	minimum delta value in ticks stored for reconfiguration
 * @max_delta_ticks:	maximum delta value in ticks stored for reconfiguration
 * @name:		ptr to clock event name
 * @rating:		variable to rate clock event devices
 * @irq:		IRQ number (only for non CPU local devices)
 * @bound_on:		Bound on CPU
 * @cpumask:		cpumask to indicate for which CPUs this device works
 * @list:		list head for the management code
 * @owner:		module reference
 */
struct clock_event_device {
	void			(*event_handler)(struct clock_event_device *);
	int			(*set_next_event)(unsigned long evt,
						  struct clock_event_device *);
	int			(*set_next_ktime)(ktime_t expires,
						  struct clock_event_device *);
	ktime_t			next_event;
	u64			max_delta_ns;
	u64			min_delta_ns;
	u32			mult;
	u32			shift;
	enum clock_event_mode	mode;
	unsigned int		features;
	unsigned long		retries;

	void			(*broadcast)(const struct cpumask *mask);
	void			(*set_mode)(enum clock_event_mode mode,
					    struct clock_event_device *);
	void			(*suspend)(struct clock_event_device *);
	void			(*resume)(struct clock_event_device *);
	unsigned long		min_delta_ticks;
	unsigned long		max_delta_ticks;

	const char		*name;
	int			rating;
	int			irq;
	int			bound_on;
	const struct cpumask	*cpumask;
	struct list_head	list;
	struct module		*owner;
} ____cacheline_aligned;

CLOCK_EVT_MODE_PERIODIC	周期触发模式，设置后按给定的周期不停地触发事件；
CLOCK_EVT_MODE_ONESHOT	单次触发模式，只在设置好的触发时刻触发一次；

static void __init samsung_clockevent_init(void)
{
	unsigned long pclk;
	unsigned long clock_rate;
	unsigned int irq_number;

	pclk = clk_get_rate(pwm.timerclk);

	samsung_timer_set_prescale(pwm.event_id, pwm.tscaler_div);
	samsung_timer_set_divisor(pwm.event_id, pwm.tdiv);

	clock_rate = pclk / (pwm.tscaler_div * pwm.tdiv);
	pwm.clock_count_per_tick = clock_rate / HZ;

	time_event_device.cpumask = cpumask_of(0);
	clockevents_config_and_register(&time_event_device,
						clock_rate, 1, pwm.tcnt_max);

	irq_number = pwm.irq[pwm.event_id];
	setup_irq(irq_number, &samsung_clock_event_irq);

	if (pwm.variant.has_tint_cstat) {
		u32 mask = (1 << pwm.event_id);
		writel(mask | (mask << 5), pwm.base + REG_TINT_CSTAT);
	}
}

static struct clock_event_device time_event_device = {
	.name		= "samsung_event_timer",
	.features	= CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
	.rating		= 200,
	.set_next_event	= samsung_set_next_event,
	.set_mode	= samsung_set_mode,
	.resume		= samsung_clockevent_resume,
};

/*
 * Must hold jiffies_lock
 */
void do_timer(unsigned long ticks)
{
	jiffies_64 += ticks;
	calc_global_load(ticks);
}

/*
 * Called from the timer interrupt handler to charge one tick to the current
 * process.  user_tick is 1 if the tick is user time, 0 for system.
 */
void update_process_times(int user_tick)
{
	struct task_struct *p = current;

	/* Note: this timer irq context must be accounted for as well. */
	account_process_tick(p, user_tick);
	run_local_timers(); //
	rcu_check_callbacks(user_tick);
#ifdef CONFIG_IRQ_WORK
	if (in_irq())
		irq_work_tick();
#endif
	scheduler_tick();
	run_posix_cpu_timers(p);
}

/*
 * Called by the local, per-CPU timer interrupt on SMP.
 */
void run_local_timers(void)
{
	hrtimer_run_queues();   //
	raise_softirq(TIMER_SOFTIRQ);   //
}

/*
 * This function runs timers and the timer-tq in bottom half context.
 */
static void run_timer_softirq(struct softirq_action *h)
{
	struct tvec_base *base = __this_cpu_read(tvec_bases);

	hrtimer_run_pending();  //

	if (time_after_eq(jiffies, base->timer_jiffies))
		__run_timers(base); //
}

/*
 * Called from timer softirq every jiffy, expire hrtimers:
 *
 * For HRT its the fall back code to run the softirq in the timer
 * softirq context in case the hrtimer initialization failed or has
 * not been done yet.
 */
void hrtimer_run_pending(void)
{
	if (hrtimer_hres_active())
		return;

	/*
	 * This _is_ ugly: We have to check in the softirq context,
	 * whether we can switch to highres and / or nohz mode. The
	 * clocksource switch happens in the timer interrupt with
	 * xtime_lock held. Notification from there only sets the
	 * check bit in the tick_oneshot code, otherwise we might
	 * deadlock vs. xtime_lock.
	 */
	if (tick_check_oneshot_change(!hrtimer_is_hres_enabled()))
		hrtimer_switch_to_hres();
}

/*
 * Called from hardirq context every jiffy
 */
void hrtimer_run_queues(void)
{
	struct timerqueue_node *node;
	struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);
	struct hrtimer_clock_base *base;
	int index, gettime = 1;

	if (hrtimer_hres_active())  //
		return;

	for (index = 0; index < HRTIMER_MAX_CLOCK_BASES; index++) {
		base = &cpu_base->clock_base[index];
		if (!timerqueue_getnext(&base->active))
			continue;

		if (gettime) {
			hrtimer_get_softirq_time(cpu_base);
			gettime = 0;
		}

		raw_spin_lock(&cpu_base->lock);

		while ((node = timerqueue_getnext(&base->active))) {
			struct hrtimer *timer;

			timer = container_of(node, struct hrtimer, node);
			if (base->softirq_time.tv64 <=
					hrtimer_get_expires_tv64(timer))
				break;

			__run_hrtimer(timer, &base->softirq_time);
		}
		raw_spin_unlock(&cpu_base->lock);
	}
}