/*
 *  linux/arch/mips/kernel/time.c
 *
 *  Copyright (C) 1991, 1992, 1995  Linus Torvalds
 *
 * This file contains the time handling details for PC-style clocks as
 * found in some MIPS systems.
 *
 */
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/param.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/interrupt.h>

#include <asm/bootinfo.h>
#include <asm/mipsregs.h>
#include <asm/io.h>
#include <asm/irq.h>

#include <linux/mc146818rtc.h>
#include <linux/timex.h>

extern volatile unsigned long lost_ticks;

/*
 * Change this if you have some constant time drift
 */
/* This is the value for the PC-style PICs. */
/* #define USECS_PER_JIFFY (1000020/HZ) */

/* This is for machines which generate the exact clock. */
#define USECS_PER_JIFFY (1000000/HZ)

/* Cycle counter value at the previous timer interrupt.. */

static unsigned int timerhi = 0, timerlo = 0;

/*
 * On MIPS only R4000 and better have a cycle counter.
 *
 * FIXME: Does playing with the RP bit in c0_status interfere with this code?
 */
static unsigned long do_fast_gettimeoffset(void)
{
    u32 count;
    unsigned long res, tmp;

    /* Last jiffy when do_fast_gettimeoffset() was called. */
    static unsigned long last_jiffies = 0;
    unsigned long quotient;

    /*
     * Cached "1/(clocks per usec)*2^32" value.
     * It has to be recalculated once each jiffy.
     */
    static unsigned long cached_quotient = 0;

    tmp = jiffies;

    quotient = cached_quotient;

    if (last_jiffies != tmp) {
	last_jiffies = tmp;
	__asm__(".set\tnoreorder\n\t"
		".set\tnoat\n\t"
		".set\tmips3\n\t"
		"lwu\t%0,%2\n\t"
		"dsll32\t$1,%1,0\n\t"
		"or\t$1,$1,%0\n\t"
		"ddivu\t$0,$1,%3\n\t"
		"mflo\t$1\n\t"
		"dsll32\t%0,%4,0\n\t"
		"nop\n\t"
		"ddivu\t$0,%0,$1\n\t"
		"mflo\t%0\n\t"
		".set\tmips0\n\t"
		".set\tat\n\t"
		".set\treorder"
      :	"=&r"(quotient)
      :	"r"(timerhi),
		"m"(timerlo),
		"r"(tmp),
		"r"(USECS_PER_JIFFY)
      :	"$1");
	cached_quotient = quotient;
    }
    /* Get last timer tick in absolute kernel time */
    count = read_32bit_cp0_register(CP0_COUNT);

    /* .. relative to previous jiffy (32 bits is enough) */
    count -= timerlo;
//printk("count: %08lx, %08lx:%08lx\n", count, timerhi, timerlo);

    __asm__("multu\t%1,%2\n\t"
	    "mfhi\t%0"
  :	    "=r"(res)
  :	    "r"(count),
	    "r"(quotient));

    /*
     * Due to possible jiffies inconsistencies, we need to check 
     * the result so that we'll get a timer that is monotonic.
     */
    if (res >= USECS_PER_JIFFY)
	res = USECS_PER_JIFFY - 1;

    return res;
}

/* This function must be called with interrupts disabled 
 * It was inspired by Steve McCanne's microtime-i386 for BSD.  -- jrs
 * 
 * However, the pc-audio speaker driver changes the divisor so that
 * it gets interrupted rather more often - it loads 64 into the
 * counter rather than 11932! This has an adverse impact on
 * do_gettimeoffset() -- it stops working! What is also not
 * good is that the interval that our timer function gets called
 * is no longer 10.0002 ms, but 9.9767 ms. To get around this
 * would require using a different timing source. Maybe someone
 * could use the RTC - I know that this can interrupt at frequencies
 * ranging from 8192Hz to 2Hz. If I had the energy, I'd somehow fix
 * it so that at startup, the timer code in sched.c would select
 * using either the RTC or the 8253 timer. The decision would be
 * based on whether there was any other device around that needed
 * to trample on the 8253. I'd set up the RTC to interrupt at 1024 Hz,
 * and then do some jiggery to have a version of do_timer that 
 * advanced the clock by 1/1024 s. Every time that reached over 1/100
 * of a second, then do all the old code. If the time was kept correct
 * then do_gettimeoffset could just return 0 - there is no low order
 * divider that can be accessed.
 *
 * Ideally, you would be able to use the RTC for the speaker driver,
 * but it appears that the speaker driver really needs interrupt more
 * often than every 120 us or so.
 *
 * Anyway, this needs more thought....          pjsg (1993-08-28)
 * 
 * If you are really that interested, you should be reading
 * comp.protocols.time.ntp!
 */

#define TICK_SIZE tick

static unsigned long do_slow_gettimeoffset(void)
{
    /*
     * This is a kludge until I find a way for the
     * DECstations without bus cycle counter. HK
     */
    return 0;
}

static unsigned long (*do_gettimeoffset) (void) = do_slow_gettimeoffset;

/*
 * This version of gettimeofday has near microsecond resolution.
 */
void do_gettimeofday(struct timeval *tv)
{
    unsigned long flags;

    save_and_cli(flags);
    *tv = xtime;
    tv->tv_usec += do_gettimeoffset();

    /*
     * xtime is atomically updated in timer_bh. lost_ticks is
     * nonzero if the timer bottom half hasnt executed yet.
     */
    if (lost_ticks)
	tv->tv_usec += USECS_PER_JIFFY;

    restore_flags(flags);

    if (tv->tv_usec >= 1000000) {
	tv->tv_usec -= 1000000;
	tv->tv_sec++;
    }
}

void do_settimeofday(struct timeval *tv)
{
    cli();
    /* This is revolting. We need to set the xtime.tv_usec
     * correctly. However, the value in this location is
     * is value at the last tick.
     * Discover what correction gettimeofday
     * would have done, and then undo it!
     */
    tv->tv_usec -= do_gettimeoffset();

    if (tv->tv_usec < 0) {
	tv->tv_usec += 1000000;
	tv->tv_sec--;
    }
    xtime = *tv;
    time_state = TIME_BAD;
    time_maxerror = MAXPHASE;
    time_esterror = MAXPHASE;
    sti();
}

/*
 * In order to set the CMOS clock precisely, set_rtc_mmss has to be
 * called 500 ms after the second nowtime has started, because when
 * nowtime is written into the registers of the CMOS clock, it will
 * jump to the next second precisely 500 ms later. Check the Motorola
 * MC146818A or Dallas DS12887 data sheet for details.
 */
static int set_rtc_mmss(unsigned long nowtime)
{
    int retval = 0;
    int real_seconds, real_minutes, cmos_minutes;
    unsigned char save_control, save_freq_select;

    save_control = CMOS_READ(RTC_CONTROL);	/* tell the clock it's being set */
    CMOS_WRITE((save_control | RTC_SET), RTC_CONTROL);

    save_freq_select = CMOS_READ(RTC_FREQ_SELECT);	/* stop and reset prescaler */
    CMOS_WRITE((save_freq_select | RTC_DIV_RESET2), RTC_FREQ_SELECT);

    cmos_minutes = CMOS_READ(RTC_MINUTES);
    if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
	BCD_TO_BIN(cmos_minutes);

    /*
     * since we're only adjusting minutes and seconds,
     * don't interfere with hour overflow. This avoids
     * messing with unknown time zones but requires your
     * RTC not to be off by more than 15 minutes
     */
    real_seconds = nowtime % 60;
    real_minutes = nowtime / 60;
    if (((abs(real_minutes - cmos_minutes) + 15) / 30) & 1)
	real_minutes += 30;	/* correct for half hour time zone */
    real_minutes %= 60;

    if (abs(real_minutes - cmos_minutes) < 30) {
	if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
	    BIN_TO_BCD(real_seconds);
	    BIN_TO_BCD(real_minutes);
	}
	CMOS_WRITE(real_seconds, RTC_SECONDS);
	CMOS_WRITE(real_minutes, RTC_MINUTES);
    } else
	retval = -1;

    /* The following flags have to be released exactly in this order,
     * otherwise the DS12887 (popular MC146818A clone with integrated
     * battery and quartz) will not reset the oscillator and will not
     * update precisely 500 ms later. You won't find this mentioned in
     * the Dallas Semiconductor data sheets, but who believes data
     * sheets anyway ...                           -- Markus Kuhn
     */
    CMOS_WRITE(save_control, RTC_CONTROL);
    CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);

    return retval;
}

/* last time the cmos clock got updated */
static long last_rtc_update = 0;

/*
 * timer_interrupt() needs to keep up the real-time clock,
 * as well as call the "do_timer()" routine every clocktick
 */
static void inline
 timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
    volatile unsigned char dummy;

    dummy = CMOS_READ(RTC_REG_C);	/* ACK RTC Interrupt */
    do_timer(regs);

    /*
     * If we have an externally synchronized Linux clock, then update
     * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
     * called as close as possible to 500 ms before the new second starts.
     */
    if (time_state != TIME_BAD && xtime.tv_sec > last_rtc_update + 660 &&
	xtime.tv_usec > 500000 - (tick >> 1) &&
	xtime.tv_usec < 500000 + (tick >> 1))
	if (set_rtc_mmss(xtime.tv_sec) == 0)
	    last_rtc_update = xtime.tv_sec;
	else
	    last_rtc_update = xtime.tv_sec - 600;	/* do it again in 60 s */
}

static void r4k_timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
    unsigned int count;

    /*
     * The cycle counter is only 32 bit which is good for about
     * a minute at current count rates of upto 150MHz or so.
     */
    count = read_32bit_cp0_register(CP0_COUNT);
    timerhi += (count < timerlo);	/* Wrap around */
    timerlo = count;

    timer_interrupt(irq, dev_id, regs);
}

/* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
 *
 * [For the Julian calendar (which was used in Russia before 1917,
 * Britain & colonies before 1752, anywhere else before 1582,
 * and is still in use by some communities) leave out the
 * -year/100+year/400 terms, and add 10.]
 *
 * This algorithm was first published by Gauss (I think).
 *
 * WARNING: this function will overflow on 2106-02-07 06:28:16 on
 * machines were long is 32-bit! (However, as time_t is signed, we
 * will already get problems at other places on 2038-01-19 03:14:08)
 */
static inline unsigned long mktime(unsigned int year, unsigned int mon,
				   unsigned int day, unsigned int hour,
				   unsigned int min, unsigned int sec)
{
    if (0 >= (int) (mon -= 2)) {	/* 1..12 -> 11,12,1..10 */
	mon += 12;		/* Puts Feb last since it has leap day */
	year -= 1;
    }
    return (((
		 (unsigned long) (year / 4 - year / 100 + year / 400 + 367 * mon / 12 + day) +
		 year * 365 - 719499
	     ) * 24 + hour	/* now have hours */
	    ) * 60 + min	/* now have minutes */
	) * 60 + sec;		/* finally seconds */
}

char cyclecounter_available;

static inline void init_cycle_counter(void)
{
    switch (mips_cputype) {
    case CPU_UNKNOWN:
    case CPU_R2000:
    case CPU_R3000:
    case CPU_R3000A:
    case CPU_R3041:
    case CPU_R3051:
    case CPU_R3052:
    case CPU_R3081:
    case CPU_R3081E:
    case CPU_R6000:
    case CPU_R6000A:
    case CPU_R8000:		/* Not shure about that one, play safe */
	cyclecounter_available = 0;
	break;
    case CPU_R4000PC:
    case CPU_R4000SC:
    case CPU_R4000MC:
    case CPU_R4200:
    case CPU_R4400PC:
    case CPU_R4400SC:
    case CPU_R4400MC:
    case CPU_R4600:
    case CPU_R10000:
    case CPU_R4300:
    case CPU_R4650:
    case CPU_R4700:
    case CPU_R5000:
    case CPU_R5000A:
    case CPU_R4640:
    case CPU_NEVADA:
	cyclecounter_available = 1;
	break;
    }
}

struct irqaction irq0 =
{timer_interrupt, SA_INTERRUPT, 0,
 "timer", NULL, NULL};


void (*board_time_init) (struct irqaction * irq);

void __init time_init(void)
{
    unsigned int year, mon, day, hour, min, sec;
    int i;

    /* The Linux interpretation of the CMOS clock register contents:
     * When the Update-In-Progress (UIP) flag goes from 1 to 0, the
     * RTC registers show the second which has precisely just started.
     * Let's hope other operating systems interpret the RTC the same way.
     */
    /* read RTC exactly on falling edge of update flag */
    for (i = 0; i < 1000000; i++)	/* may take up to 1 second... */
	if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP)
	    break;
    for (i = 0; i < 1000000; i++)	/* must try at least 2.228 ms */
	if (!(CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP))
	    break;
    do {			/* Isn't this overkill ? UIP above should guarantee consistency */
	sec = CMOS_READ(RTC_SECONDS);
	min = CMOS_READ(RTC_MINUTES);
	hour = CMOS_READ(RTC_HOURS);
	day = CMOS_READ(RTC_DAY_OF_MONTH);
	mon = CMOS_READ(RTC_MONTH);
	year = CMOS_READ(RTC_YEAR);
    } while (sec != CMOS_READ(RTC_SECONDS));
    if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
	BCD_TO_BIN(sec);
	BCD_TO_BIN(min);
	BCD_TO_BIN(hour);
	BCD_TO_BIN(day);
	BCD_TO_BIN(mon);
	BCD_TO_BIN(year);
    }
    /*
     * The DECstation RTC is used as a TOY (Time Of Year).
     * The PROM will reset the year to either '70, '71 or '72.
     * This hack will only work until Dec 31 2001.
     */
    year += 1927;

    xtime.tv_sec = mktime(year, mon, day, hour, min, sec);
    xtime.tv_usec = 0;

    init_cycle_counter();

    if (cyclecounter_available) {
	write_32bit_cp0_register(CP0_COUNT, 0);
	do_gettimeoffset = do_fast_gettimeoffset;
	irq0.handler = r4k_timer_interrupt;
    }
    board_time_init(&irq0);
}