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rtc.c

/* MN10300 RTC management
 *
 * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * 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/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/mc146818rtc.h>
#include <linux/bcd.h>
#include <linux/timex.h>
#include <asm/rtc-regs.h>
#include <asm/rtc.h>

DEFINE_SPINLOCK(rtc_lock);
EXPORT_SYMBOL(rtc_lock);

/* last time the RTC got updated */
static long last_rtc_update;

/* time for RTC to update itself in ioclks */
static unsigned long mn10300_rtc_update_period;

/*
 * read the current RTC time
 */
unsigned long __init get_initial_rtc_time(void)
{
      struct rtc_time tm;

      get_rtc_time(&tm);

      return mktime(tm.tm_year, tm.tm_mon, tm.tm_mday,
                  tm.tm_hour, tm.tm_min, tm.tm_sec);
}

/*
 * 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.
 *
 * BUG: This routine does not handle hour overflow properly; it just
 *      sets the minutes. Usually you'll only notice that after reboot!
 */
static int set_rtc_mmss(unsigned long nowtime)
{
      unsigned char save_control, save_freq_select;
      int retval = 0;
      int real_seconds, real_minutes, cmos_minutes;

      /* gets recalled with irq locally disabled */
      spin_lock(&rtc_lock);
      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)
            cmos_minutes = bcd2bin(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)
            /* correct for half hour time zone */
            real_minutes += 30;
      real_minutes %= 60;

      if (abs(real_minutes - cmos_minutes) < 30) {
            if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
                  real_seconds = bin2bcd(real_seconds);
                  real_minutes = bin2bcd(real_minutes);
            }
            CMOS_WRITE(real_seconds, RTC_SECONDS);
            CMOS_WRITE(real_minutes, RTC_MINUTES);
      } else {
            printk(KERN_WARNING
                   "set_rtc_mmss: can't update from %d to %d\n",
                   cmos_minutes, real_minutes);
            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);
      spin_unlock(&rtc_lock);

      return retval;
}

void check_rtc_time(void)
{
      /* the RTC clock just finished ticking over again this second
       * - if we have an externally synchronized Linux clock, then update
       *   RTC 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_status & STA_UNSYNC) == 0 &&
          xtime.tv_sec > last_rtc_update + 660 &&
          xtime.tv_nsec / 1000 >= 500000 - ((unsigned) TICK_SIZE) / 2 &&
          xtime.tv_nsec / 1000 <= 500000 + ((unsigned) TICK_SIZE) / 2
          ) {
            if (set_rtc_mmss(xtime.tv_sec) == 0)
                  last_rtc_update = xtime.tv_sec;
            else
                  /* do it again in 60s */
                  last_rtc_update = xtime.tv_sec - 600;
      }
}

/*
 * calibrate the TSC clock against the RTC
 */
void __init calibrate_clock(void)
{
      unsigned long count0, counth, count1;
      unsigned char status;

      /* make sure the RTC is running and is set to operate in 24hr mode */
      status = RTSRC;
      RTCRB |= RTCRB_SET;
      RTCRB |= RTCRB_TM_24HR;
      RTCRA |= RTCRA_DVR;
      RTCRA &= ~RTCRA_DVR;
      RTCRB &= ~RTCRB_SET;

      /* work out the clock speed by counting clock cycles between ends of
       * the RTC update cycle - track the RTC through one complete update
       * cycle (1 second)
       */
      startup_timestamp_counter();

      while (!(RTCRA & RTCRA_UIP)) {}
      while ((RTCRA & RTCRA_UIP)) {}

      count0 = TMTSCBC;

      while (!(RTCRA & RTCRA_UIP)) {}

      counth = TMTSCBC;

      while ((RTCRA & RTCRA_UIP)) {}

      count1 = TMTSCBC;

      shutdown_timestamp_counter();

      MN10300_TSCCLK = count0 - count1; /* the timers count down */
      mn10300_rtc_update_period = counth - count1;
      MN10300_TSC_PER_HZ = MN10300_TSCCLK / HZ;
}

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