/*
   * linux/kernel/time/tick-broadcast-hrtimer.c
   * This file emulates a local clock event device
   * via a pseudo clock device.
   */
  #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/clockchips.h>
  #include <linux/sched.h>
  #include <linux/smp.h>
  #include <linux/module.h>
  
  #include "tick-internal.h"
  
  static struct hrtimer bctimer;
  
  static void bc_set_mode(enum clock_event_mode mode,
  			struct clock_event_device *bc)
  {
  	switch (mode) {
  	case CLOCK_EVT_MODE_SHUTDOWN:
  		/*
  		 * Note, we cannot cancel the timer here as we might
  		 * run into the following live lock scenario:
  		 *
  		 * cpu 0		cpu1
  		 * lock(broadcast_lock);
  		 *			hrtimer_interrupt()
  		 *			bc_handler()
  		 *			   tick_handle_oneshot_broadcast();
  		 *			    lock(broadcast_lock);
  		 * hrtimer_cancel()
  		 *  wait_for_callback()
  		 */
  		hrtimer_try_to_cancel(&bctimer);
  		break;
  	default:
  		break;
  	}
  }
  
  /*
   * This is called from the guts of the broadcast code when the cpu
   * which is about to enter idle has the earliest broadcast timer event.
   */
  static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
  {
  	/*
  	 * We try to cancel the timer first. If the callback is on
  	 * flight on some other cpu then we let it handle it. If we
  	 * were able to cancel the timer nothing can rearm it as we
  	 * own broadcast_lock.
  	 *
  	 * However we can also be called from the event handler of
  	 * ce_broadcast_hrtimer itself when it expires. We cannot
  	 * restart the timer because we are in the callback, but we
  	 * can set the expiry time and let the callback return
  	 * HRTIMER_RESTART.
  	 */
  	if (hrtimer_try_to_cancel(&bctimer) >= 0) {
  		hrtimer_start(&bctimer, expires, HRTIMER_MODE_ABS_PINNED);
  		/* Bind the "device" to the cpu */
  		bc->bound_on = smp_processor_id();
  	} else if (bc->bound_on == smp_processor_id()) {
  		hrtimer_set_expires(&bctimer, expires);
  	}
  	return 0;
  }
  
  static struct clock_event_device ce_broadcast_hrtimer = {
  	.set_mode		= bc_set_mode,
  	.set_next_ktime		= bc_set_next,
  	.features		= CLOCK_EVT_FEAT_ONESHOT |
  				  CLOCK_EVT_FEAT_KTIME |
  				  CLOCK_EVT_FEAT_HRTIMER,
  	.rating			= 0,
  	.bound_on		= -1,
  	.min_delta_ns		= 1,
  	.max_delta_ns		= KTIME_MAX,
  	.min_delta_ticks	= 1,

  	.max_delta_ticks	= ULONG_MAX,

  	.mult			= 1,
  	.shift			= 0,
  	.cpumask		= cpu_all_mask,
  };
  
  static enum hrtimer_restart bc_handler(struct hrtimer *t)
  {
  	ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer);
  
  	if (ce_broadcast_hrtimer.next_event.tv64 == KTIME_MAX)
  		return HRTIMER_NORESTART;
  
  	return HRTIMER_RESTART;
  }
  
  void tick_setup_hrtimer_broadcast(void)
  {
  	hrtimer_init(&bctimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
  	bctimer.function = bc_handler;
  	clockevents_register_device(&ce_broadcast_hrtimer);
  }