/*
 * i8253.c  8253/PIT functions
 *
 */
#include <linux/clockchips.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/jiffies.h>
#include <linux/module.h>
#include <linux/spinlock.h>

#include <asm/delay.h>
#include <asm/i8253.h>
#include <asm/io.h>
#include <asm/time.h>

DEFINE_SPINLOCK(i8253_lock);

/*
 * Initialize the PIT timer.
 *
 * This is also called after resume to bring the PIT into operation again.
 */
static void init_pit_timer(enum clock_event_mode mode,
                           struct clock_event_device *evt)
{
        unsigned long flags;

        spin_lock_irqsave(&i8253_lock, flags);

        switch(mode) {
        case CLOCK_EVT_MODE_PERIODIC:
                /* binary, mode 2, LSB/MSB, ch 0 */
                outb_p(0x34, PIT_MODE);
                outb_p(LATCH & 0xff , PIT_CH0); /* LSB */
                outb(LATCH >> 8 , PIT_CH0);     /* MSB */
                break;

        case CLOCK_EVT_MODE_SHUTDOWN:
        case CLOCK_EVT_MODE_UNUSED:
                if (evt->mode == CLOCK_EVT_MODE_PERIODIC ||
                    evt->mode == CLOCK_EVT_MODE_ONESHOT) {
                        outb_p(0x30, PIT_MODE);
                        outb_p(0, PIT_CH0);
                        outb_p(0, PIT_CH0);
                }
                break;

        case CLOCK_EVT_MODE_ONESHOT:
                /* One shot setup */
                outb_p(0x38, PIT_MODE);
                break;

        case CLOCK_EVT_MODE_RESUME:
                /* Nothing to do here */
                break;
        }
        spin_unlock_irqrestore(&i8253_lock, flags);
}

/*
 * Program the next event in oneshot mode
 *
 * Delta is given in PIT ticks
 */
static int pit_next_event(unsigned long delta, struct clock_event_device *evt)
{
        unsigned long flags;

        spin_lock_irqsave(&i8253_lock, flags);
        outb_p(delta & 0xff , PIT_CH0); /* LSB */
        outb(delta >> 8 , PIT_CH0);     /* MSB */
        spin_unlock_irqrestore(&i8253_lock, flags);

        return 0;
}

/*
 * On UP the PIT can serve all of the possible timer functions. On SMP systems
 * it can be solely used for the global tick.
 *
 * The profiling and update capabilites are switched off once the local apic is
 * registered. This mechanism replaces the previous #ifdef LOCAL_APIC -
 * !using_apic_timer decisions in do_timer_interrupt_hook()
 */
struct clock_event_device pit_clockevent = {
        .name           = "pit",
        .features       = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
        .set_mode       = init_pit_timer,
        .set_next_event = pit_next_event,
        .irq            = 0,
};

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

        return IRQ_HANDLED;
}

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

/*
 * Initialize the conversion factor and the min/max deltas of the clock event
 * structure and register the clock event source with the framework.
 */
void __init setup_pit_timer(void)
{
        struct clock_event_device *cd = &pit_clockevent;
        unsigned int cpu = smp_processor_id();

        /*
         * Start pit with the boot cpu mask and make it global after the
         * IO_APIC has been initialized.
         */
        cd->cpumask = cpumask_of_cpu(cpu);
        clockevent_set_clock(cd, CLOCK_TICK_RATE);
        cd->max_delta_ns = clockevent_delta2ns(0x7FFF, cd);
        cd->min_delta_ns = clockevent_delta2ns(0xF, cd);
        clockevents_register_device(cd);

        irq0.mask = cpumask_of_cpu(cpu);
        setup_irq(0, &irq0);
}

/*
 * Since the PIT overflows every tick, its not very useful
 * to just read by itself. So use jiffies to emulate a free
 * running counter:
 */
static cycle_t pit_read(void)
{
        unsigned long flags;
        int count;
        u32 jifs;
        static int old_count;
        static u32 old_jifs;

        spin_lock_irqsave(&i8253_lock, flags);
        /*
         * Although our caller may have the read side of xtime_lock,
         * this is now a seqlock, and we are cheating in this routine
         * by having side effects on state that we cannot undo if
         * there is a collision on the seqlock and our caller has to
         * retry.  (Namely, old_jifs and old_count.)  So we must treat
         * jiffies as volatile despite the lock.  We read jiffies
         * before latching the timer count to guarantee that although
         * the jiffies value might be older than the count (that is,
         * the counter may underflow between the last point where
         * jiffies was incremented and the point where we latch the
         * count), it cannot be newer.
         */
        jifs = jiffies;
        outb_p(0x00, PIT_MODE); /* latch the count ASAP */
        count = inb_p(PIT_CH0); /* read the latched count */
        count |= inb_p(PIT_CH0) << 8;

        /* VIA686a test code... reset the latch if count > max + 1 */
        if (count > LATCH) {
                outb_p(0x34, PIT_MODE);
                outb_p(LATCH & 0xff, PIT_CH0);
                outb(LATCH >> 8, PIT_CH0);
                count = LATCH - 1;
        }

        /*
         * It's possible for count to appear to go the wrong way for a
         * couple of reasons:
         *
         *  1. The timer counter underflows, but we haven't handled the
         *     resulting interrupt and incremented jiffies yet.
         *  2. Hardware problem with the timer, not giving us continuous time,
         *     the counter does small "jumps" upwards on some Pentium systems,
         *     (see c't 95/10 page 335 for Neptun bug.)
         *
         * Previous attempts to handle these cases intelligently were
         * buggy, so we just do the simple thing now.
         */
        if (count > old_count && jifs == old_jifs) {
                count = old_count;
        }
        old_count = count;
        old_jifs = jifs;

        spin_unlock_irqrestore(&i8253_lock, flags);

        count = (LATCH - 1) - count;

        return (cycle_t)(jifs * LATCH) + count;
}

static struct clocksource clocksource_pit = {
        .name   = "pit",
        .rating = 110,
        .read   = pit_read,
        .mask   = CLOCKSOURCE_MASK(32),
        .mult   = 0,
        .shift  = 20,
};

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

        clocksource_pit.mult = clocksource_hz2mult(CLOCK_TICK_RATE, 20);
        return clocksource_register(&clocksource_pit);
}
arch_initcall(init_pit_clocksource);