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time.c

/*
 * Common time routines among all ppc machines.
 *
 * Written by Cort Dougan (cort@cs.nmt.edu) to merge
 * Paul Mackerras' version and mine for PReP and Pmac.
 * MPC8xx/MBX changes by Dan Malek (dmalek@jlc.net).
 *
 * First round of bugfixes by Gabriel Paubert (paubert@iram.es)
 * to make clock more stable (2.4.0-test5). The only thing
 * that this code assumes is that the timebases have been synchronized
 * by firmware on SMP and are never stopped (never do sleep
 * on SMP then, nap and doze are OK).
 *
 * TODO (not necessarily in this file):
 * - improve precision and reproducibility of timebase frequency
 * measurement at boot time.
 * - get rid of xtime_lock for gettimeofday (generic kernel problem
 * to be implemented on all architectures for SMP scalability and
 * eventually implementing gettimeofday without entering the kernel).
 * - put all time/clock related variables in a single structure
 * to minimize number of cache lines touched by gettimeofday()
 * - for astronomical applications: add a new function to get
 * non ambiguous timestamps even around leap seconds. This needs
 * a new timestamp format and a good name.
 *
 *
 * The following comment is partially obsolete (at least the long wait
 * is no more a valid reason):
 * Since the MPC8xx has a programmable interrupt timer, I decided to
 * use that rather than the decrementer.  Two reasons: 1.) the clock
 * frequency is low, causing 2.) a long wait in the timer interrupt
 *          while ((d = get_dec()) == dval)
 * loop.  The MPC8xx can be driven from a variety of input clocks,
 * so a number of assumptions have been made here because the kernel
 * parameter HZ is a constant.  We assume (correctly, today :-) that
 * the MPC8xx on the MBX board is driven from a 32.768 kHz crystal.
 * This is then divided by 4, providing a 8192 Hz clock into the PIT.
 * Since it is not possible to get a nice 100 Hz clock out of this, without
 * creating a software PLL, I have set HZ to 128.  -- Dan
 *
 * 1997-09-10  Updated NTP code according to technical memorandum Jan '96
 *             "A Kernel Model for Precision Timekeeping" by Dave Mills
 */

#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/param.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/timex.h>
#include <linux/kernel_stat.h>
#include <linux/mc146818rtc.h>
#include <linux/time.h>
#include <linux/init.h>
#include <linux/profile.h>

#include <asm/io.h>
#include <asm/nvram.h>
#include <asm/cache.h>
#include <asm/8xx_immap.h>
#include <asm/machdep.h>
#include <asm/irq_regs.h>

#include <asm/time.h>

unsigned long disarm_decr[NR_CPUS];

extern struct timezone sys_tz;

/* keep track of when we need to update the rtc */
time_t last_rtc_update;

/* The decrementer counts down by 128 every 128ns on a 601. */
#define DECREMENTER_COUNT_601 (1000000000 / HZ)

unsigned tb_ticks_per_jiffy;
unsigned tb_to_us;
unsigned tb_last_stamp;
unsigned long tb_to_ns_scale;

/* used for timezone offset */
static long timezone_offset;

DEFINE_SPINLOCK(rtc_lock);

EXPORT_SYMBOL(rtc_lock);

/* Timer interrupt helper function */
static inline int tb_delta(unsigned *jiffy_stamp) {
      int delta;
      if (__USE_RTC()) {
            delta = get_rtcl();
            if (delta < *jiffy_stamp) *jiffy_stamp -= 1000000000;
            delta -= *jiffy_stamp;
      } else {
            delta = get_tbl() - *jiffy_stamp;
      }
      return delta;
}

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

      if (in_lock_functions(pc))
            return regs->link;

      return pc;
}
EXPORT_SYMBOL(profile_pc);
#endif

void wakeup_decrementer(void)
{
      set_dec(tb_ticks_per_jiffy);
      /* No currently-supported powerbook has a 601,
       * so use get_tbl, not native
       */
      last_jiffy_stamp(0) = tb_last_stamp = get_tbl();
}

/*
 * timer_interrupt - gets called when the decrementer overflows,
 * with interrupts disabled.
 * We set it up to overflow again in 1/HZ seconds.
 */
void timer_interrupt(struct pt_regs * regs)
{
      struct pt_regs *old_regs;
      int next_dec;
      unsigned long cpu = smp_processor_id();
      unsigned jiffy_stamp = last_jiffy_stamp(cpu);
      extern void do_IRQ(struct pt_regs *);

      if (atomic_read(&ppc_n_lost_interrupts) != 0)
            do_IRQ(regs);

      old_regs = set_irq_regs(regs);
      irq_enter();

      while ((next_dec = tb_ticks_per_jiffy - tb_delta(&jiffy_stamp)) <= 0) {
            jiffy_stamp += tb_ticks_per_jiffy;
            
            profile_tick(CPU_PROFILING);
            update_process_times(user_mode(regs));

            if (smp_processor_id())
                  continue;

            /* We are in an interrupt, no need to save/restore flags */
            write_seqlock(&xtime_lock);
            tb_last_stamp = jiffy_stamp;
            do_timer(1);

            /*
             * update the rtc when needed, this should be performed on the
             * right fraction of a second. Half or full second ?
             * Full second works on mk48t59 clocks, others need testing.
             * Note that this update is basically only used through
             * the adjtimex system calls. Setting the HW clock in
             * any other way is a /dev/rtc and userland business.
             * This is still wrong by -0.5/+1.5 jiffies because of the
             * timer interrupt resolution and possible delay, but here we
             * hit a quantization limit which can only be solved by higher
             * resolution timers and decoupling time management from timer
             * interrupts. This is also wrong on the clocks
             * which require being written at the half second boundary.
             * We should have an rtc call that only sets the minutes and
             * seconds like on Intel to avoid problems with non UTC clocks.
             */
            if ( ppc_md.set_rtc_time && ntp_synced() &&
                 xtime.tv_sec - last_rtc_update >= 659 &&
                 abs((xtime.tv_nsec / 1000) - (1000000-1000000/HZ)) < 500000/HZ) {
                  if (ppc_md.set_rtc_time(xtime.tv_sec+1 + timezone_offset) == 0)
                        last_rtc_update = xtime.tv_sec+1;
                  else
                        /* Try again one minute later */
                        last_rtc_update += 60;
            }
            write_sequnlock(&xtime_lock);
      }
      if ( !disarm_decr[smp_processor_id()] )
            set_dec(next_dec);
      last_jiffy_stamp(cpu) = jiffy_stamp;

      if (ppc_md.heartbeat && !ppc_md.heartbeat_count--)
            ppc_md.heartbeat();

      irq_exit();
      set_irq_regs(old_regs);
}

/*
 * This version of gettimeofday has microsecond resolution.
 */
void do_gettimeofday(struct timeval *tv)
{
      unsigned long flags;
      unsigned long seq;
      unsigned delta, usec, sec;

      do {
            seq = read_seqbegin_irqsave(&xtime_lock, flags);
            sec = xtime.tv_sec;
            usec = (xtime.tv_nsec / 1000);
            delta = tb_ticks_since(tb_last_stamp);
#ifdef CONFIG_SMP
            /* As long as timebases are not in sync, gettimeofday can only
             * have jiffy resolution on SMP.
             */
            if (!smp_tb_synchronized)
                  delta = 0;
#endif /* CONFIG_SMP */
      } while (read_seqretry_irqrestore(&xtime_lock, seq, flags));

      usec += mulhwu(tb_to_us, delta);
      while (usec >= 1000000) {
            sec++;
            usec -= 1000000;
      }
      tv->tv_sec = sec;
      tv->tv_usec = usec;
}

EXPORT_SYMBOL(do_gettimeofday);

int do_settimeofday(struct timespec *tv)
{
      time_t wtm_sec, new_sec = tv->tv_sec;
      long wtm_nsec, new_nsec = tv->tv_nsec;
      unsigned long flags;
      int tb_delta;

      if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
            return -EINVAL;

      write_seqlock_irqsave(&xtime_lock, flags);
      /* Updating the RTC is not the job of this code. If the time is
       * stepped under NTP, the RTC will be update after STA_UNSYNC
       * is cleared. Tool like clock/hwclock either copy the RTC
       * to the system time, in which case there is no point in writing
       * to the RTC again, or write to the RTC but then they don't call
       * settimeofday to perform this operation. Note also that
       * we don't touch the decrementer since:
       * a) it would lose timer interrupt synchronization on SMP
       * (if it is working one day)
       * b) it could make one jiffy spuriously shorter or longer
       * which would introduce another source of uncertainty potentially
       * harmful to relatively short timers.
       */

      /* This works perfectly on SMP only if the tb are in sync but
       * guarantees an error < 1 jiffy even if they are off by eons,
       * still reasonable when gettimeofday resolution is 1 jiffy.
       */
      tb_delta = tb_ticks_since(last_jiffy_stamp(smp_processor_id()));

      new_nsec -= 1000 * mulhwu(tb_to_us, tb_delta);

      wtm_sec  = wall_to_monotonic.tv_sec + (xtime.tv_sec - new_sec);
      wtm_nsec = wall_to_monotonic.tv_nsec + (xtime.tv_nsec - new_nsec);

      set_normalized_timespec(&xtime, new_sec, new_nsec);
      set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec);

      /* In case of a large backwards jump in time with NTP, we want the
       * clock to be updated as soon as the PLL is again in lock.
       */
      last_rtc_update = new_sec - 658;

      ntp_clear();
      write_sequnlock_irqrestore(&xtime_lock, flags);
      clock_was_set();
      return 0;
}

EXPORT_SYMBOL(do_settimeofday);

/* This function is only called on the boot processor */
void __init time_init(void)
{
      time_t sec, old_sec;
      unsigned old_stamp, stamp, elapsed;

        if (ppc_md.time_init != NULL)
                timezone_offset = ppc_md.time_init();

      if (__USE_RTC()) {
            /* 601 processor: dec counts down by 128 every 128ns */
            tb_ticks_per_jiffy = DECREMENTER_COUNT_601;
            /* mulhwu_scale_factor(1000000000, 1000000) is 0x418937 */
            tb_to_us = 0x418937;
        } else {
                ppc_md.calibrate_decr();
            tb_to_ns_scale = mulhwu(tb_to_us, 1000 << 10);
      }

      /* Now that the decrementer is calibrated, it can be used in case the
       * clock is stuck, but the fact that we have to handle the 601
       * makes things more complex. Repeatedly read the RTC until the
       * next second boundary to try to achieve some precision.  If there
       * is no RTC, we still need to set tb_last_stamp and
       * last_jiffy_stamp(cpu 0) to the current stamp.
       */
      stamp = get_native_tbl();
      if (ppc_md.get_rtc_time) {
            sec = ppc_md.get_rtc_time();
            elapsed = 0;
            do {
                  old_stamp = stamp;
                  old_sec = sec;
                  stamp = get_native_tbl();
                  if (__USE_RTC() && stamp < old_stamp)
                        old_stamp -= 1000000000;
                  elapsed += stamp - old_stamp;
                  sec = ppc_md.get_rtc_time();
            } while ( sec == old_sec && elapsed < 2*HZ*tb_ticks_per_jiffy);
            if (sec==old_sec)
                  printk("Warning: real time clock seems stuck!\n");
            xtime.tv_sec = sec;
            xtime.tv_nsec = 0;
            /* No update now, we just read the time from the RTC ! */
            last_rtc_update = xtime.tv_sec;
      }
      last_jiffy_stamp(0) = tb_last_stamp = stamp;

      /* Not exact, but the timer interrupt takes care of this */
      set_dec(tb_ticks_per_jiffy);

      /* If platform provided a timezone (pmac), we correct the time */
        if (timezone_offset) {
            sys_tz.tz_minuteswest = -timezone_offset / 60;
            sys_tz.tz_dsttime = 0;
            xtime.tv_sec -= timezone_offset;
        }
        set_normalized_timespec(&wall_to_monotonic,
                                -xtime.tv_sec, -xtime.tv_nsec);
}

#define FEBRUARY        2
#define     STARTOFTIME       1970
#define SECDAY                86400L
#define SECYR                 (SECDAY * 365)

/*
 * Note: this is wrong for 2100, but our signed 32-bit time_t will
 * have overflowed long before that, so who cares.  -- paulus
 */
#define     leapyear(year)          ((year) % 4 == 0)
#define     days_in_year(a)   (leapyear(a) ? 366 : 365)
#define     days_in_month(a)  (month_days[(a) - 1])

static int month_days[12] = {
      31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
};

void to_tm(int tim, struct rtc_time * tm)
{
      register int i;
      register long hms, day, gday;

      gday = day = tim / SECDAY;
      hms = tim % SECDAY;

      /* Hours, minutes, seconds are easy */
      tm->tm_hour = hms / 3600;
      tm->tm_min = (hms % 3600) / 60;
      tm->tm_sec = (hms % 3600) % 60;

      /* Number of years in days */
      for (i = STARTOFTIME; day >= days_in_year(i); i++)
            day -= days_in_year(i);
      tm->tm_year = i;

      /* Number of months in days left */
      if (leapyear(tm->tm_year))
            days_in_month(FEBRUARY) = 29;
      for (i = 1; day >= days_in_month(i); i++)
            day -= days_in_month(i);
      days_in_month(FEBRUARY) = 28;
      tm->tm_mon = i;

      /* Days are what is left over (+1) from all that. */
      tm->tm_mday = day + 1;

      /*
       * Determine the day of week. Jan. 1, 1970 was a Thursday.
       */
      tm->tm_wday = (gday + 4) % 7;
}

/* Auxiliary function to compute scaling factors */
/* Actually the choice of a timebase running at 1/4 the of the bus
 * frequency giving resolution of a few tens of nanoseconds is quite nice.
 * It makes this computation very precise (27-28 bits typically) which
 * is optimistic considering the stability of most processor clock
 * oscillators and the precision with which the timebase frequency
 * is measured but does not harm.
 */
unsigned mulhwu_scale_factor(unsigned inscale, unsigned outscale) {
      unsigned mlt=0, tmp, err;
      /* No concern for performance, it's done once: use a stupid
       * but safe and compact method to find the multiplier.
       */
      for (tmp = 1U<<31; tmp != 0; tmp >>= 1) {
            if (mulhwu(inscale, mlt|tmp) < outscale) mlt|=tmp;
      }
      /* We might still be off by 1 for the best approximation.
       * A side effect of this is that if outscale is too large
       * the returned value will be zero.
       * Many corner cases have been checked and seem to work,
       * some might have been forgotten in the test however.
       */
      err = inscale*(mlt+1);
      if (err <= inscale/2) mlt++;
      return mlt;
}

unsigned long long sched_clock(void)
{
      unsigned long lo, hi, hi2;
      unsigned long long tb;

      if (!__USE_RTC()) {
            do {
                  hi = get_tbu();
                  lo = get_tbl();
                  hi2 = get_tbu();
            } while (hi2 != hi);
            tb = ((unsigned long long) hi << 32) | lo;
            tb = (tb * tb_to_ns_scale) >> 10;
      } else {
            do {
                  hi = get_rtcu();
                  lo = get_rtcl();
                  hi2 = get_rtcu();
            } while (hi2 != hi);
            tb = ((unsigned long long) hi) * 1000000000 + lo;
      }
      return tb;
}

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