// SPDX-License-Identifier: GPL-2.0

  #include "sched.h"

  /*
   * idle-task scheduling class.
   *
   * (NOTE: these are not related to SCHED_IDLE tasks which are

   *  handled in sched/fair.c)

   */

  #ifdef CONFIG_SMP

  static int

  select_task_rq_idle(struct task_struct *p, int cpu, int sd_flag, int flags)

  {
  	return task_cpu(p); /* IDLE tasks as never migrated */
  }
  #endif /* CONFIG_SMP */

  /*
   * Idle tasks are unconditionally rescheduled:
   */

  static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int flags)

  {

  	resched_curr(rq);

  }

  static struct task_struct *

  pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)

  {

  	put_prev_task(rq, prev);

  	update_idle_core(rq);

  	schedstat_inc(rq->sched_goidle);

  	return rq->idle;
  }
  
  /*
   * It is not legal to sleep in the idle task - print a warning
   * message if some code attempts to do it:
   */
  static void

  dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)

  {

  	raw_spin_unlock_irq(&rq->lock);

  	printk(KERN_ERR "bad: scheduling from the idle thread!
  ");

  	dump_stack();

  	raw_spin_lock_irq(&rq->lock);

  }

  static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)

  {

  	rq_last_tick_reset(rq);

  }

  static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)

  {
  }

  static void set_curr_task_idle(struct rq *rq)
  {
  }

  static void switched_to_idle(struct rq *rq, struct task_struct *p)

  {

  	BUG();

  }

  static void
  prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio)

  {

  	BUG();

  }

  static unsigned int get_rr_interval_idle(struct rq *rq, struct task_struct *task)

  {
  	return 0;
  }

  static void update_curr_idle(struct rq *rq)
  {
  }

  /*
   * Simple, special scheduling class for the per-CPU idle tasks:
   */

  const struct sched_class idle_sched_class = {

  	/* .next is NULL */

  	/* no enqueue/yield_task for idle tasks */
  
  	/* dequeue is not valid, we print a debug message there: */
  	.dequeue_task		= dequeue_task_idle,
  
  	.check_preempt_curr	= check_preempt_curr_idle,
  
  	.pick_next_task		= pick_next_task_idle,
  	.put_prev_task		= put_prev_task_idle,

  #ifdef CONFIG_SMP

  	.select_task_rq		= select_task_rq_idle,

  	.set_cpus_allowed	= set_cpus_allowed_common,

  #endif

  	.set_curr_task          = set_curr_task_idle,

  	.task_tick		= task_tick_idle,

  	.get_rr_interval	= get_rr_interval_idle,

  	.prio_changed		= prio_changed_idle,
  	.switched_to		= switched_to_idle,

  	.update_curr		= update_curr_idle,

  };