/*
   * Functions related to interrupt-poll handling in the block layer. This
   * is similar to NAPI for network devices.
   */
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/init.h>
  #include <linux/bio.h>

  #include <linux/interrupt.h>
  #include <linux/cpu.h>

  #include <linux/irq_poll.h>

  #include <linux/delay.h>

  static unsigned int irq_poll_budget __read_mostly = 256;

  static DEFINE_PER_CPU(struct list_head, blk_cpu_iopoll);
  
  /**

   * irq_poll_sched - Schedule a run of the iopoll handler

   * @iop:      The parent iopoll structure
   *
   * Description:

   *     Add this irq_poll structure to the pending poll list and trigger the

   *     raise of the blk iopoll softirq.

   **/

  void irq_poll_sched(struct irq_poll *iop)

  {
  	unsigned long flags;

  	if (test_bit(IRQ_POLL_F_DISABLE, &iop->state))
  		return;

  	if (test_and_set_bit(IRQ_POLL_F_SCHED, &iop->state))

  		return;

  	local_irq_save(flags);

  	list_add_tail(&iop->list, this_cpu_ptr(&blk_cpu_iopoll));

  	__raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);

  	local_irq_restore(flags);
  }

  EXPORT_SYMBOL(irq_poll_sched);

  
  /**

   * __irq_poll_complete - Mark this @iop as un-polled again

   * @iop:      The parent iopoll structure
   *
   * Description:

   *     See irq_poll_complete(). This function must be called with interrupts

   *     disabled.

   **/

  static void __irq_poll_complete(struct irq_poll *iop)

  {
  	list_del(&iop->list);

  	smp_mb__before_atomic();

  	clear_bit_unlock(IRQ_POLL_F_SCHED, &iop->state);

  }

  
  /**

   * irq_poll_complete - Mark this @iop as un-polled again

   * @iop:      The parent iopoll structure
   *
   * Description:

   *     If a driver consumes less than the assigned budget in its run of the
   *     iopoll handler, it'll end the polled mode by calling this function. The

   *     iopoll handler will not be invoked again before irq_poll_sched()

   *     is called.

   **/

  void irq_poll_complete(struct irq_poll *iop)

  {
  	unsigned long flags;
  
  	local_irq_save(flags);

  	__irq_poll_complete(iop);

  	local_irq_restore(flags);
  }

  EXPORT_SYMBOL(irq_poll_complete);

  static void __latent_entropy irq_poll_softirq(struct softirq_action *h)

  {

  	struct list_head *list = this_cpu_ptr(&blk_cpu_iopoll);

  	int rearm = 0, budget = irq_poll_budget;

  	unsigned long start_time = jiffies;

  
  	local_irq_disable();
  
  	while (!list_empty(list)) {

  		struct irq_poll *iop;

  		int work, weight;
  
  		/*
  		 * If softirq window is exhausted then punt.
  		 */
  		if (budget <= 0 || time_after(jiffies, start_time)) {
  			rearm = 1;
  			break;
  		}
  
  		local_irq_enable();
  
  		/* Even though interrupts have been re-enabled, this
  		 * access is safe because interrupts can only add new
  		 * entries to the tail of this list, and only ->poll()
  		 * calls can remove this head entry from the list.
  		 */

  		iop = list_entry(list->next, struct irq_poll, list);

  
  		weight = iop->weight;
  		work = 0;

  		if (test_bit(IRQ_POLL_F_SCHED, &iop->state))

  			work = iop->poll(iop, weight);
  
  		budget -= work;
  
  		local_irq_disable();

  		/*
  		 * Drivers must not modify the iopoll state, if they
  		 * consume their assigned weight (or more, some drivers can't
  		 * easily just stop processing, they have to complete an
  		 * entire mask of commands).In such cases this code
  		 * still "owns" the iopoll instance and therefore can

  		 * move the instance around on the list at-will.
  		 */
  		if (work >= weight) {

  			if (test_bit(IRQ_POLL_F_DISABLE, &iop->state))

  				__irq_poll_complete(iop);

  			else
  				list_move_tail(&iop->list, list);
  		}
  	}
  
  	if (rearm)

  		__raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);

  
  	local_irq_enable();
  }
  
  /**

   * irq_poll_disable - Disable iopoll on this @iop

   * @iop:      The parent iopoll structure
   *
   * Description:
   *     Disable io polling and wait for any pending callbacks to have completed.
   **/

  void irq_poll_disable(struct irq_poll *iop)

  {

  	set_bit(IRQ_POLL_F_DISABLE, &iop->state);
  	while (test_and_set_bit(IRQ_POLL_F_SCHED, &iop->state))

  		msleep(1);

  	clear_bit(IRQ_POLL_F_DISABLE, &iop->state);

  }

  EXPORT_SYMBOL(irq_poll_disable);

  
  /**

   * irq_poll_enable - Enable iopoll on this @iop

   * @iop:      The parent iopoll structure
   *
   * Description:

   *     Enable iopoll on this @iop. Note that the handler run will not be
   *     scheduled, it will only mark it as active.

   **/

  void irq_poll_enable(struct irq_poll *iop)

  {

  	BUG_ON(!test_bit(IRQ_POLL_F_SCHED, &iop->state));

  	smp_mb__before_atomic();

  	clear_bit_unlock(IRQ_POLL_F_SCHED, &iop->state);

  }

  EXPORT_SYMBOL(irq_poll_enable);

  
  /**

   * irq_poll_init - Initialize this @iop

   * @iop:      The parent iopoll structure
   * @weight:   The default weight (or command completion budget)
   * @poll_fn:  The handler to invoke
   *
   * Description:

   *     Initialize and enable this irq_poll structure.

   **/

  void irq_poll_init(struct irq_poll *iop, int weight, irq_poll_fn *poll_fn)

  {
  	memset(iop, 0, sizeof(*iop));
  	INIT_LIST_HEAD(&iop->list);
  	iop->weight = weight;
  	iop->poll = poll_fn;

  }

  EXPORT_SYMBOL(irq_poll_init);

  static int irq_poll_cpu_dead(unsigned int cpu)

  {
  	/*
  	 * If a CPU goes away, splice its entries to the current CPU
  	 * and trigger a run of the softirq
  	 */

  	local_irq_disable();
  	list_splice_init(&per_cpu(blk_cpu_iopoll, cpu),
  			 this_cpu_ptr(&blk_cpu_iopoll));
  	__raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
  	local_irq_enable();

  	return 0;

  }

  static __init int irq_poll_setup(void)

  {
  	int i;
  
  	for_each_possible_cpu(i)
  		INIT_LIST_HEAD(&per_cpu(blk_cpu_iopoll, i));

  	open_softirq(IRQ_POLL_SOFTIRQ, irq_poll_softirq);

  	cpuhp_setup_state_nocalls(CPUHP_IRQ_POLL_DEAD, "irq_poll:dead", NULL,
  				  irq_poll_cpu_dead);

  	return 0;
  }

  subsys_initcall(irq_poll_setup);