drivers/rtc/rtc-mc146818-lib.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 #include <linux/bcd.h>
   3 #include <linux/delay.h>
   4 #include <linux/export.h>
   5 #include <linux/mc146818rtc.h>
   6
   7 #ifdef CONFIG_ACPI
   8 #include <linux/acpi.h>
   9 #endif
  10
  11 unsigned int mc146818_get_time(struct rtc_time *time)
  12 {
  13         unsigned char ctrl;
  14         unsigned long flags;
  15         unsigned char century = 0;
  16         bool retry;
  17
  18 #ifdef CONFIG_MACH_DECSTATION
  19         unsigned int real_year;
  20 #endif
  21
  22 again:
  23         spin_lock_irqsave(&rtc_lock, flags);
  24         /*
  25          * Check whether there is an update in progress during which the
  26          * readout is unspecified. The maximum update time is ~2ms. Poll
  27          * every msec for completion.
  28          *
  29          * Store the second value before checking UIP so a long lasting NMI
  30          * which happens to hit after the UIP check cannot make an update
  31          * cycle invisible.
  32          */
  33         time->tm_sec = CMOS_READ(RTC_SECONDS);
  34
  35         if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) {
  36                 spin_unlock_irqrestore(&rtc_lock, flags);
  37                 mdelay(1);
  38                 goto again;
  39         }
  40
  41         /* Revalidate the above readout */
  42         if (time->tm_sec != CMOS_READ(RTC_SECONDS)) {
  43                 spin_unlock_irqrestore(&rtc_lock, flags);
  44                 goto again;
  45         }
  46
  47         /*
  48          * Only the values that we read from the RTC are set. We leave
  49          * tm_wday, tm_yday and tm_isdst untouched. Even though the
  50          * RTC has RTC_DAY_OF_WEEK, we ignore it, as it is only updated
  51          * by the RTC when initially set to a non-zero value.
  52          */
  53         time->tm_min = CMOS_READ(RTC_MINUTES);
  54         time->tm_hour = CMOS_READ(RTC_HOURS);
  55         time->tm_mday = CMOS_READ(RTC_DAY_OF_MONTH);
  56         time->tm_mon = CMOS_READ(RTC_MONTH);
  57         time->tm_year = CMOS_READ(RTC_YEAR);
  58 #ifdef CONFIG_MACH_DECSTATION
  59         real_year = CMOS_READ(RTC_DEC_YEAR);
  60 #endif
  61 #ifdef CONFIG_ACPI
  62         if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
  63             acpi_gbl_FADT.century)
  64                 century = CMOS_READ(acpi_gbl_FADT.century);
  65 #endif
  66         ctrl = CMOS_READ(RTC_CONTROL);
  67         /*
  68          * Check for the UIP bit again. If it is set now then
  69          * the above values may contain garbage.
  70          */
  71         retry = CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP;
  72         /*
  73          * A NMI might have interrupted the above sequence so check whether
  74          * the seconds value has changed which indicates that the NMI took
  75          * longer than the UIP bit was set. Unlikely, but possible and
  76          * there is also virt...
  77          */
  78         retry |= time->tm_sec != CMOS_READ(RTC_SECONDS);
  79
  80         spin_unlock_irqrestore(&rtc_lock, flags);
  81
  82         if (retry)
  83                 goto again;
  84
  85         if (!(ctrl & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
  86         {
  87                 time->tm_sec = bcd2bin(time->tm_sec);
  88                 time->tm_min = bcd2bin(time->tm_min);
  89                 time->tm_hour = bcd2bin(time->tm_hour);
  90                 time->tm_mday = bcd2bin(time->tm_mday);
  91                 time->tm_mon = bcd2bin(time->tm_mon);
  92                 time->tm_year = bcd2bin(time->tm_year);
  93                 century = bcd2bin(century);
  94         }
  95
  96 #ifdef CONFIG_MACH_DECSTATION
  97         time->tm_year += real_year - 72;
  98 #endif
  99
 100         if (century > 20)
 101                 time->tm_year += (century - 19) * 100;
 102
 103         /*
 104          * Account for differences between how the RTC uses the values
 105          * and how they are defined in a struct rtc_time;
 106          */
 107         if (time->tm_year <= 69)
 108                 time->tm_year += 100;
 109
 110         time->tm_mon--;
 111
 112         return RTC_24H;
 113 }
 114 EXPORT_SYMBOL_GPL(mc146818_get_time);
 115
 116 /* Set the current date and time in the real time clock. */
 117 int mc146818_set_time(struct rtc_time *time)
 118 {
 119         unsigned long flags;
 120         unsigned char mon, day, hrs, min, sec;
 121         unsigned char save_control, save_freq_select;
 122         unsigned int yrs;
 123 #ifdef CONFIG_MACH_DECSTATION
 124         unsigned int real_yrs, leap_yr;
 125 #endif
 126         unsigned char century = 0;
 127
 128         yrs = time->tm_year;
 129         mon = time->tm_mon + 1;   /* tm_mon starts at zero */
 130         day = time->tm_mday;
 131         hrs = time->tm_hour;
 132         min = time->tm_min;
 133         sec = time->tm_sec;
 134
 135         if (yrs > 255)  /* They are unsigned */
 136                 return -EINVAL;
 137
 138 #ifdef CONFIG_MACH_DECSTATION
 139         real_yrs = yrs;
 140         leap_yr = ((!((yrs + 1900) % 4) && ((yrs + 1900) % 100)) ||
 141                         !((yrs + 1900) % 400));
 142         yrs = 72;
 143
 144         /*
 145          * We want to keep the year set to 73 until March
 146          * for non-leap years, so that Feb, 29th is handled
 147          * correctly.
 148          */
 149         if (!leap_yr && mon < 3) {
 150                 real_yrs--;
 151                 yrs = 73;
 152         }
 153 #endif
 154
 155 #ifdef CONFIG_ACPI
 156         if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
 157             acpi_gbl_FADT.century) {
 158                 century = (yrs + 1900) / 100;
 159                 yrs %= 100;
 160         }
 161 #endif
 162
 163         /* These limits and adjustments are independent of
 164          * whether the chip is in binary mode or not.
 165          */
 166         if (yrs > 169)
 167                 return -EINVAL;
 168
 169         if (yrs >= 100)
 170                 yrs -= 100;
 171
 172         if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY)
 173             || RTC_ALWAYS_BCD) {
 174                 sec = bin2bcd(sec);
 175                 min = bin2bcd(min);
 176                 hrs = bin2bcd(hrs);
 177                 day = bin2bcd(day);
 178                 mon = bin2bcd(mon);
 179                 yrs = bin2bcd(yrs);
 180                 century = bin2bcd(century);
 181         }
 182
 183         spin_lock_irqsave(&rtc_lock, flags);
 184         save_control = CMOS_READ(RTC_CONTROL);
 185         CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
 186         save_freq_select = CMOS_READ(RTC_FREQ_SELECT);
 187         CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);
 188
 189 #ifdef CONFIG_MACH_DECSTATION
 190         CMOS_WRITE(real_yrs, RTC_DEC_YEAR);
 191 #endif
 192         CMOS_WRITE(yrs, RTC_YEAR);
 193         CMOS_WRITE(mon, RTC_MONTH);
 194         CMOS_WRITE(day, RTC_DAY_OF_MONTH);
 195         CMOS_WRITE(hrs, RTC_HOURS);
 196         CMOS_WRITE(min, RTC_MINUTES);
 197         CMOS_WRITE(sec, RTC_SECONDS);
 198 #ifdef CONFIG_ACPI
 199         if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
 200             acpi_gbl_FADT.century)
 201                 CMOS_WRITE(century, acpi_gbl_FADT.century);
 202 #endif
 203
 204         CMOS_WRITE(save_control, RTC_CONTROL);
 205         CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
 206
 207         spin_unlock_irqrestore(&rtc_lock, flags);
 208
 209         return 0;
 210 }
 211 EXPORT_SYMBOL_GPL(mc146818_set_time);