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time.c

/* MN10300 Low level time management
 *
 * Copyright (C) 2007-2008 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 * - Derived from arch/i386/kernel/time.c
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/interrupt.h>
#include <linux/time.h>
#include <linux/init.h>
#include <linux/smp.h>
#include <linux/profile.h>
#include <linux/cnt32_to_63.h>
#include <asm/irq.h>
#include <asm/div64.h>
#include <asm/processor.h>
#include <asm/intctl-regs.h>
#include <asm/rtc.h>

#ifdef CONFIG_MN10300_RTC
unsigned long mn10300_ioclk;        /* system I/O clock frequency */
unsigned long mn10300_iobclk;       /* system I/O clock frequency */
unsigned long mn10300_tsc_per_HZ;   /* number of ioclks per jiffy */
#endif /* CONFIG_MN10300_RTC */

static unsigned long mn10300_last_tsc;    /* time-stamp counter at last time
                               * interrupt occurred */

static irqreturn_t timer_interrupt(int irq, void *dev_id);

static struct irqaction timer_irq = {
      .handler    = timer_interrupt,
      .flags            = IRQF_DISABLED | IRQF_SHARED | IRQF_TIMER,
      .mask       = CPU_MASK_NONE,
      .name       = "timer",
};

static unsigned long sched_clock_multiplier;

/*
 * scheduler clock - returns current time in nanosec units.
 */
unsigned long long sched_clock(void)
{
      union {
            unsigned long long ll;
            unsigned l[2];
      } tsc64, result;
      unsigned long tsc, tmp;
      unsigned product[3]; /* 96-bit intermediate value */

      /* read the TSC value
       */
      tsc = 0 - get_cycles(); /* get_cycles() counts down */

      /* expand to 64-bits.
       * - sched_clock() must be called once a minute or better or the
       *   following will go horribly wrong - see cnt32_to_63()
       */
      tsc64.ll = cnt32_to_63(tsc) & 0x7fffffffffffffffULL;

      /* scale the 64-bit TSC value to a nanosecond value via a 96-bit
       * intermediate
       */
      asm("mulu   %2,%0,%3,%0 \n"   /* LSW * mult ->  0:%3:%0 */
          "mulu   %2,%1,%2,%1 \n"   /* MSW * mult -> %2:%1:0 */
          "add    %3,%1       \n"
          "addc   0,%2        \n"   /* result in %2:%1:%0 */
          : "=r"(product[0]), "=r"(product[1]), "=r"(product[2]), "=r"(tmp)
          :  "0"(tsc64.l[0]),  "1"(tsc64.l[1]),  "2"(sched_clock_multiplier)
          : "cc");

      result.l[0] = product[1] << 16 | product[0] >> 16;
      result.l[1] = product[2] << 16 | product[1] >> 16;

      return result.ll;
}

/*
 * initialise the scheduler clock
 */
static void __init mn10300_sched_clock_init(void)
{
      sched_clock_multiplier =
            __muldiv64u(NSEC_PER_SEC, 1 << 16, MN10300_TSCCLK);
}

/*
 * advance the kernel's time keeping clocks (xtime and jiffies)
 * - we use Timer 0 & 1 cascaded as a clock to nudge us the next time
 *   there's a need to update
 */
static irqreturn_t timer_interrupt(int irq, void *dev_id)
{
      unsigned tsc, elapse;

      write_seqlock(&xtime_lock);

      while (tsc = get_cycles(),
             elapse = mn10300_last_tsc - tsc, /* time elapsed since last
                                     * tick */
             elapse > MN10300_TSC_PER_HZ
             ) {
            mn10300_last_tsc -= MN10300_TSC_PER_HZ;

            /* advance the kernel's time tracking system */
            profile_tick(CPU_PROFILING);
            do_timer(1);
            check_rtc_time();
      }

      write_sequnlock(&xtime_lock);

      update_process_times(user_mode(get_irq_regs()));

      return IRQ_HANDLED;
}

/*
 * initialise the various timers used by the main part of the kernel
 */
void __init time_init(void)
{
      /* we need the prescalar running to be able to use IOCLK/8
       * - IOCLK runs at 1/4 (ST5 open) or 1/8 (ST5 closed) internal CPU clock
       * - IOCLK runs at Fosc rate (crystal speed)
       */
      TMPSCNT |= TMPSCNT_ENABLE;

      startup_timestamp_counter();

      printk(KERN_INFO
             "timestamp counter I/O clock running at %lu.%02lu"
             " (calibrated against RTC)\n",
             MN10300_TSCCLK / 1000000, (MN10300_TSCCLK / 10000) % 100);

      xtime.tv_sec = get_initial_rtc_time();
      xtime.tv_nsec = 0;

      mn10300_last_tsc = TMTSCBC;

      /* use timer 0 & 1 cascaded to tick at as close to HZ as possible */
      setup_irq(TMJCIRQ, &timer_irq);

      set_intr_level(TMJCIRQ, TMJCICR_LEVEL);

      startup_jiffies_counter();

#ifdef CONFIG_MN10300_WD_TIMER
      /* start the watchdog timer */
      watchdog_go();
#endif

      mn10300_sched_clock_init();
}

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