i8253.c

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/*
 * i8253.c  8253/PIT functions
 *
 */
#include <linux/clockchips.h>
#include <linux/i8253.h>
#include <linux/export.h>
#include <linux/smp.h>
#include <linux/irq.h>

#include <asm/time.h>

static irqreturn_t timer_interrupt(int irq, void *dev_id)
{
    i8253_clockevent.event_handler(&i8253_clockevent);

    return IRQ_HANDLED;
}

static struct irqaction irq0  = {
    .handler = timer_interrupt,
    .flags = IRQF_NOBALANCING | IRQF_TIMER,
    .name = "timer"
};

void __init setup_pit_timer(void)
{
    clockevent_i8253_init(true);
    setup_irq(0, &irq0);
}

static int __init init_pit_clocksource(void)
{
    if (num_possible_cpus() > 1) /* PIT does not scale! */
        return 0;

    return clocksource_i8253_init();
}
arch_initcall(init_pit_clocksource);