/*
 * 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 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_notify(struct notifier_block *self,
                                 unsigned long action, void *hcpu)
{
        /*
         * If a CPU goes away, splice its entries to the current CPU
         * and trigger a run of the softirq
         */
        if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
                int cpu = (unsigned long) hcpu;

                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 NOTIFY_OK;
}

static struct notifier_block irq_poll_cpu_notifier = {
        .notifier_call  = irq_poll_cpu_notify,
};

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);
        register_hotcpu_notifier(&irq_poll_cpu_notifier);
        return 0;
}
subsys_initcall(irq_poll_setup);