/*
 *  linux/arch/parisc/kernel/time.c
 *
 *  Copyright (C) 1991, 1992, 1995  Linus Torvalds
 *  Modifications for ARM (C) 1994, 1995, 1996,1997 Russell King
 *  Copyright (C) 1999 SuSE GmbH, (Philipp Rumpf, prumpf@tux.org)
 *
 * 1994-07-02  Alan Modra
 *             fixed set_rtc_mmss, fixed time.year for >= 2000, new mktime
 * 1998-12-20  Updated NTP code according to technical memorandum Jan '96
 *             "A Kernel Model for Precision Timekeeping" by Dave Mills
 */
#include <linux/errno.h>
#include <linux/module.h>
#include <linux/rtc.h>
#include <linux/sched.h>
#include <linux/sched_clock.h>
#include <linux/kernel.h>
#include <linux/param.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/time.h>
#include <linux/init.h>
#include <linux/smp.h>
#include <linux/profile.h>
#include <linux/clocksource.h>
#include <linux/platform_device.h>
#include <linux/ftrace.h>

#include <asm/uaccess.h>
#include <asm/io.h>
#include <asm/irq.h>
#include <asm/page.h>
#include <asm/param.h>
#include <asm/pdc.h>
#include <asm/led.h>

#include <linux/timex.h>

static unsigned long clocktick __read_mostly;   /* timer cycles per tick */

/*
 * We keep time on PA-RISC Linux by using the Interval Timer which is
 * a pair of registers; one is read-only and one is write-only; both
 * accessed through CR16.  The read-only register is 32 or 64 bits wide,
 * and increments by 1 every CPU clock tick.  The architecture only
 * guarantees us a rate between 0.5 and 2, but all implementations use a
 * rate of 1.  The write-only register is 32-bits wide.  When the lowest
 * 32 bits of the read-only register compare equal to the write-only
 * register, it raises a maskable external interrupt.  Each processor has
 * an Interval Timer of its own and they are not synchronised.  
 *
 * We want to generate an interrupt every 1/HZ seconds.  So we program
 * CR16 to interrupt every @clocktick cycles.  The it_value in cpu_data
 * is programmed with the intended time of the next tick.  We can be
 * held off for an arbitrarily long period of time by interrupts being
 * disabled, so we may miss one or more ticks.
 */
irqreturn_t __irq_entry timer_interrupt(int irq, void *dev_id)
{
        unsigned long now, now2;
        unsigned long next_tick;
        unsigned long cycles_elapsed, ticks_elapsed = 1;
        unsigned long cycles_remainder;
        unsigned int cpu = smp_processor_id();
        struct cpuinfo_parisc *cpuinfo = &per_cpu(cpu_data, cpu);

        /* gcc can optimize for "read-only" case with a local clocktick */
        unsigned long cpt = clocktick;

        profile_tick(CPU_PROFILING);

        /* Initialize next_tick to the expected tick time. */
        next_tick = cpuinfo->it_value;

        /* Get current cycle counter (Control Register 16). */
        now = mfctl(16);

        cycles_elapsed = now - next_tick;

        if ((cycles_elapsed >> 6) < cpt) {
                /* use "cheap" math (add/subtract) instead
                 * of the more expensive div/mul method
                 */
                cycles_remainder = cycles_elapsed;
                while (cycles_remainder > cpt) {
                        cycles_remainder -= cpt;
                        ticks_elapsed++;
                }
        } else {
                /* TODO: Reduce this to one fdiv op */
                cycles_remainder = cycles_elapsed % cpt;
                ticks_elapsed += cycles_elapsed / cpt;
        }

        /* convert from "division remainder" to "remainder of clock tick" */
        cycles_remainder = cpt - cycles_remainder;

        /* Determine when (in CR16 cycles) next IT interrupt will fire.
         * We want IT to fire modulo clocktick even if we miss/skip some.
         * But those interrupts don't in fact get delivered that regularly.
         */
        next_tick = now + cycles_remainder;

        cpuinfo->it_value = next_tick;

        /* Program the IT when to deliver the next interrupt.
         * Only bottom 32-bits of next_tick are writable in CR16!
         */
        mtctl(next_tick, 16);

        /* Skip one clocktick on purpose if we missed next_tick.
         * The new CR16 must be "later" than current CR16 otherwise
         * itimer would not fire until CR16 wrapped - e.g 4 seconds
         * later on a 1Ghz processor. We'll account for the missed
         * tick on the next timer interrupt.
         *
         * "next_tick - now" will always give the difference regardless
         * if one or the other wrapped. If "now" is "bigger" we'll end up
         * with a very large unsigned number.
         */
        now2 = mfctl(16);
        if (next_tick - now2 > cpt)
                mtctl(next_tick+cpt, 16);

#if 1
/*
 * GGG: DEBUG code for how many cycles programming CR16 used.
 */
        if (unlikely(now2 - now > 0x3000))      /* 12K cycles */
                printk (KERN_CRIT "timer_interrupt(CPU %d): SLOW! 0x%lx cycles!"
                        " cyc %lX rem %lX "
                        " next/now %lX/%lX\n",
                        cpu, now2 - now, cycles_elapsed, cycles_remainder,
                        next_tick, now );
#endif

        /* Can we differentiate between "early CR16" (aka Scenario 1) and
         * "long delay" (aka Scenario 3)? I don't think so.
         *
         * Timer_interrupt will be delivered at least a few hundred cycles
         * after the IT fires. But it's arbitrary how much time passes
         * before we call it "late". I've picked one second.
         *
         * It's important NO printk's are between reading CR16 and
         * setting up the next value. May introduce huge variance.
         */
        if (unlikely(ticks_elapsed > HZ)) {
                /* Scenario 3: very long delay?  bad in any case */
                printk (KERN_CRIT "timer_interrupt(CPU %d): delayed!"
                        " cycles %lX rem %lX "
                        " next/now %lX/%lX\n",
                        cpu,
                        cycles_elapsed, cycles_remainder,
                        next_tick, now );
        }

        /* Done mucking with unreliable delivery of interrupts.
         * Go do system house keeping.
         */

        if (!--cpuinfo->prof_counter) {
                cpuinfo->prof_counter = cpuinfo->prof_multiplier;
                update_process_times(user_mode(get_irq_regs()));
        }

        if (cpu == 0)
                xtime_update(ticks_elapsed);

        return IRQ_HANDLED;
}


unsigned long profile_pc(struct pt_regs *regs)
{
        unsigned long pc = instruction_pointer(regs);

        if (regs->gr[0] & PSW_N)
                pc -= 4;

#ifdef CONFIG_SMP
        if (in_lock_functions(pc))
                pc = regs->gr[2];
#endif

        return pc;
}
EXPORT_SYMBOL(profile_pc);


/* clock source code */

static cycle_t notrace read_cr16(struct clocksource *cs)
{
        return get_cycles();
}

static struct clocksource clocksource_cr16 = {
        .name                   = "cr16",
        .rating                 = 300,
        .read                   = read_cr16,
        .mask                   = CLOCKSOURCE_MASK(BITS_PER_LONG),
        .flags                  = CLOCK_SOURCE_IS_CONTINUOUS,
};

void __init start_cpu_itimer(void)
{
        unsigned int cpu = smp_processor_id();
        unsigned long next_tick = mfctl(16) + clocktick;

        mtctl(next_tick, 16);           /* kick off Interval Timer (CR16) */

        per_cpu(cpu_data, cpu).it_value = next_tick;
}

#if IS_ENABLED(CONFIG_RTC_DRV_GENERIC)
static int rtc_generic_get_time(struct device *dev, struct rtc_time *tm)
{
        struct pdc_tod tod_data;

        memset(tm, 0, sizeof(*tm));
        if (pdc_tod_read(&tod_data) < 0)
                return -EOPNOTSUPP;

        /* we treat tod_sec as unsigned, so this can work until year 2106 */
        rtc_time64_to_tm(tod_data.tod_sec, tm);
        return rtc_valid_tm(tm);
}

static int rtc_generic_set_time(struct device *dev, struct rtc_time *tm)
{
        time64_t secs = rtc_tm_to_time64(tm);

        if (pdc_tod_set(secs, 0) < 0)
                return -EOPNOTSUPP;

        return 0;
}

static const struct rtc_class_ops rtc_generic_ops = {
        .read_time = rtc_generic_get_time,
        .set_time = rtc_generic_set_time,
};

static int __init rtc_init(void)
{
        struct platform_device *pdev;

        pdev = platform_device_register_data(NULL, "rtc-generic", -1,
                                             &rtc_generic_ops,
                                             sizeof(rtc_generic_ops));

        return PTR_ERR_OR_ZERO(pdev);
}
device_initcall(rtc_init);
#endif

void read_persistent_clock(struct timespec *ts)
{
        static struct pdc_tod tod_data;
        if (pdc_tod_read(&tod_data) == 0) {
                ts->tv_sec = tod_data.tod_sec;
                ts->tv_nsec = tod_data.tod_usec * 1000;
        } else {
                printk(KERN_ERR "Error reading tod clock\n");
                ts->tv_sec = 0;
                ts->tv_nsec = 0;
        }
}


static u64 notrace read_cr16_sched_clock(void)
{
        return get_cycles();
}


/*
 * timer interrupt and sched_clock() initialization
 */

void __init time_init(void)
{
        unsigned long cr16_hz;

        clocktick = (100 * PAGE0->mem_10msec) / HZ;
        start_cpu_itimer();     /* get CPU 0 started */

        cr16_hz = 100 * PAGE0->mem_10msec;  /* Hz */

        /* register at clocksource framework */
        clocksource_register_hz(&clocksource_cr16, cr16_hz);

        /* register as sched_clock source */
        sched_clock_register(read_cr16_sched_clock, BITS_PER_LONG, cr16_hz);
}