linux/arch/mn10300/kernel/rtc.c
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   1/* MN10300 RTC management
   2 *
   3 * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
   4 * Written by David Howells (dhowells@redhat.com)
   5 *
   6 * This program is free software; you can redistribute it and/or
   7 * modify it under the terms of the GNU General Public Licence
   8 * as published by the Free Software Foundation; either version
   9 * 2 of the Licence, or (at your option) any later version.
  10 */
  11#include <linux/kernel.h>
  12#include <linux/module.h>
  13#include <linux/init.h>
  14#include <linux/mc146818rtc.h>
  15#include <linux/bcd.h>
  16#include <linux/timex.h>
  17#include <asm/rtc-regs.h>
  18#include <asm/rtc.h>
  19
  20DEFINE_SPINLOCK(rtc_lock);
  21EXPORT_SYMBOL(rtc_lock);
  22
  23/* last time the RTC got updated */
  24static long last_rtc_update;
  25
  26/* time for RTC to update itself in ioclks */
  27static unsigned long mn10300_rtc_update_period;
  28
  29/*
  30 * read the current RTC time
  31 */
  32unsigned long __init get_initial_rtc_time(void)
  33{
  34        struct rtc_time tm;
  35
  36        get_rtc_time(&tm);
  37
  38        return mktime(tm.tm_year, tm.tm_mon, tm.tm_mday,
  39                      tm.tm_hour, tm.tm_min, tm.tm_sec);
  40}
  41
  42/*
  43 * In order to set the CMOS clock precisely, set_rtc_mmss has to be called 500
  44 * ms after the second nowtime has started, because when nowtime is written
  45 * into the registers of the CMOS clock, it will jump to the next second
  46 * precisely 500 ms later.  Check the Motorola MC146818A or Dallas DS12887 data
  47 * sheet for details.
  48 *
  49 * BUG: This routine does not handle hour overflow properly; it just
  50 *      sets the minutes. Usually you'll only notice that after reboot!
  51 */
  52static int set_rtc_mmss(unsigned long nowtime)
  53{
  54        unsigned char save_control, save_freq_select;
  55        int retval = 0;
  56        int real_seconds, real_minutes, cmos_minutes;
  57
  58        /* gets recalled with irq locally disabled */
  59        spin_lock(&rtc_lock);
  60        save_control = CMOS_READ(RTC_CONTROL); /* tell the clock it's being
  61                                                * set */
  62        CMOS_WRITE(save_control | RTC_SET, RTC_CONTROL);
  63
  64        save_freq_select = CMOS_READ(RTC_FREQ_SELECT); /* stop and reset
  65                                                        * prescaler */
  66        CMOS_WRITE(save_freq_select | RTC_DIV_RESET2, RTC_FREQ_SELECT);
  67
  68        cmos_minutes = CMOS_READ(RTC_MINUTES);
  69        if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
  70                BCD_TO_BIN(cmos_minutes);
  71
  72        /*
  73         * since we're only adjusting minutes and seconds,
  74         * don't interfere with hour overflow. This avoids
  75         * messing with unknown time zones but requires your
  76         * RTC not to be off by more than 15 minutes
  77         */
  78        real_seconds = nowtime % 60;
  79        real_minutes = nowtime / 60;
  80        if (((abs(real_minutes - cmos_minutes) + 15) / 30) & 1)
  81                /* correct for half hour time zone */
  82                real_minutes += 30;
  83        real_minutes %= 60;
  84
  85        if (abs(real_minutes - cmos_minutes) < 30) {
  86                if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
  87                        BIN_TO_BCD(real_seconds);
  88                        BIN_TO_BCD(real_minutes);
  89                }
  90                CMOS_WRITE(real_seconds, RTC_SECONDS);
  91                CMOS_WRITE(real_minutes, RTC_MINUTES);
  92        } else {
  93                printk(KERN_WARNING
  94                       "set_rtc_mmss: can't update from %d to %d\n",
  95                       cmos_minutes, real_minutes);
  96                retval = -1;
  97        }
  98
  99        /* The following flags have to be released exactly in this order,
 100         * otherwise the DS12887 (popular MC146818A clone with integrated
 101         * battery and quartz) will not reset the oscillator and will not
 102         * update precisely 500 ms later. You won't find this mentioned in
 103         * the Dallas Semiconductor data sheets, but who believes data
 104         * sheets anyway ...                           -- Markus Kuhn
 105         */
 106        CMOS_WRITE(save_control, RTC_CONTROL);
 107        CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
 108        spin_unlock(&rtc_lock);
 109
 110        return retval;
 111}
 112
 113void check_rtc_time(void)
 114{
 115        /* the RTC clock just finished ticking over again this second
 116         * - if we have an externally synchronized Linux clock, then update
 117         *   RTC clock accordingly every ~11 minutes. set_rtc_mmss() has to be
 118         *   called as close as possible to 500 ms before the new second starts.
 119         */
 120        if ((time_status & STA_UNSYNC) == 0 &&
 121            xtime.tv_sec > last_rtc_update + 660 &&
 122            xtime.tv_nsec / 1000 >= 500000 - ((unsigned) TICK_SIZE) / 2 &&
 123            xtime.tv_nsec / 1000 <= 500000 + ((unsigned) TICK_SIZE) / 2
 124            ) {
 125                if (set_rtc_mmss(xtime.tv_sec) == 0)
 126                        last_rtc_update = xtime.tv_sec;
 127                else
 128                        /* do it again in 60s */
 129                        last_rtc_update = xtime.tv_sec - 600;
 130        }
 131}
 132
 133/*
 134 * calibrate the TSC clock against the RTC
 135 */
 136void __init calibrate_clock(void)
 137{
 138        unsigned long count0, counth, count1;
 139        unsigned char status;
 140
 141        /* make sure the RTC is running and is set to operate in 24hr mode */
 142        status = RTSRC;
 143        RTCRB |= RTCRB_SET;
 144        RTCRB |= RTCRB_TM_24HR;
 145        RTCRA |= RTCRA_DVR;
 146        RTCRA &= ~RTCRA_DVR;
 147        RTCRB &= ~RTCRB_SET;
 148
 149        /* work out the clock speed by counting clock cycles between ends of
 150         * the RTC update cycle - track the RTC through one complete update
 151         * cycle (1 second)
 152         */
 153        startup_timestamp_counter();
 154
 155        while (!(RTCRA & RTCRA_UIP)) {}
 156        while ((RTCRA & RTCRA_UIP)) {}
 157
 158        count0 = TMTSCBC;
 159
 160        while (!(RTCRA & RTCRA_UIP)) {}
 161
 162        counth = TMTSCBC;
 163
 164        while ((RTCRA & RTCRA_UIP)) {}
 165
 166        count1 = TMTSCBC;
 167
 168        shutdown_timestamp_counter();
 169
 170        MN10300_TSCCLK = count0 - count1; /* the timers count down */
 171        mn10300_rtc_update_period = counth - count1;
 172        MN10300_TSC_PER_HZ = MN10300_TSCCLK / HZ;
 173}
 174