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 /*
  12  * Returns true if a clock update is in progress
  13  */
  14 static inline unsigned char mc146818_is_updating(void)
  15 {
  16         unsigned char uip;
  17         unsigned long flags;
  18
  19         spin_lock_irqsave(&rtc_lock, flags);
  20         uip = (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP);
  21         spin_unlock_irqrestore(&rtc_lock, flags);
  22         return uip;
  23 }
  24
  25 unsigned int mc146818_get_time(struct rtc_time *time)
  26 {
  27         unsigned char ctrl;
  28         unsigned long flags;
  29         unsigned char century = 0;
  30
  31 #ifdef CONFIG_MACH_DECSTATION
  32         unsigned int real_year;
  33 #endif
  34
  35         /*
  36          * read RTC once any update in progress is done. The update
  37          * can take just over 2ms. We wait 20ms. There is no need to
  38          * to poll-wait (up to 1s - eeccch) for the falling edge of RTC_UIP.
  39          * If you need to know *exactly* when a second has started, enable
  40          * periodic update complete interrupts, (via ioctl) and then
  41          * immediately read /dev/rtc which will block until you get the IRQ.
  42          * Once the read clears, read the RTC time (again via ioctl). Easy.
  43          */
  44         if (mc146818_is_updating())
  45                 mdelay(20);
  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         spin_lock_irqsave(&rtc_lock, flags);
  54         time->tm_sec = CMOS_READ(RTC_SECONDS);
  55         time->tm_min = CMOS_READ(RTC_MINUTES);
  56         time->tm_hour = CMOS_READ(RTC_HOURS);
  57         time->tm_mday = CMOS_READ(RTC_DAY_OF_MONTH);
  58         time->tm_mon = CMOS_READ(RTC_MONTH);
  59         time->tm_year = CMOS_READ(RTC_YEAR);
  60 #ifdef CONFIG_MACH_DECSTATION
  61         real_year = CMOS_READ(RTC_DEC_YEAR);
  62 #endif
  63 #ifdef CONFIG_ACPI
  64         if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
  65             acpi_gbl_FADT.century)
  66                 century = CMOS_READ(acpi_gbl_FADT.century);
  67 #endif
  68         ctrl = CMOS_READ(RTC_CONTROL);
  69         spin_unlock_irqrestore(&rtc_lock, flags);
  70
  71         if (!(ctrl & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
  72         {
  73                 time->tm_sec = bcd2bin(time->tm_sec);
  74                 time->tm_min = bcd2bin(time->tm_min);
  75                 time->tm_hour = bcd2bin(time->tm_hour);
  76                 time->tm_mday = bcd2bin(time->tm_mday);
  77                 time->tm_mon = bcd2bin(time->tm_mon);
  78                 time->tm_year = bcd2bin(time->tm_year);
  79                 century = bcd2bin(century);
  80         }
  81
  82 #ifdef CONFIG_MACH_DECSTATION
  83         time->tm_year += real_year - 72;
  84 #endif
  85
  86         if (century > 19)
  87                 time->tm_year += (century - 19) * 100;
  88
  89         /*
  90          * Account for differences between how the RTC uses the values
  91          * and how they are defined in a struct rtc_time;
  92          */
  93         if (time->tm_year <= 69)
  94                 time->tm_year += 100;
  95
  96         time->tm_mon--;
  97
  98         return RTC_24H;
  99 }
 100 EXPORT_SYMBOL_GPL(mc146818_get_time);
 101
 102 /* AMD systems don't allow access to AltCentury with DV1 */
 103 static bool apply_amd_register_a_behavior(void)
 104 {
 105 #ifdef CONFIG_X86
 106         if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
 107             boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
 108                 return true;
 109 #endif
 110         return false;
 111 }
 112
 113 /* Set the current date and time in the real time clock. */
 114 int mc146818_set_time(struct rtc_time *time)
 115 {
 116         unsigned long flags;
 117         unsigned char mon, day, hrs, min, sec;
 118         unsigned char save_control, save_freq_select;
 119         unsigned int yrs;
 120 #ifdef CONFIG_MACH_DECSTATION
 121         unsigned int real_yrs, leap_yr;
 122 #endif
 123         unsigned char century = 0;
 124
 125         yrs = time->tm_year;
 126         mon = time->tm_mon + 1;   /* tm_mon starts at zero */
 127         day = time->tm_mday;
 128         hrs = time->tm_hour;
 129         min = time->tm_min;
 130         sec = time->tm_sec;
 131
 132         if (yrs > 255)  /* They are unsigned */
 133                 return -EINVAL;
 134
 135         spin_lock_irqsave(&rtc_lock, flags);
 136 #ifdef CONFIG_MACH_DECSTATION
 137         real_yrs = yrs;
 138         leap_yr = ((!((yrs + 1900) % 4) && ((yrs + 1900) % 100)) ||
 139                         !((yrs + 1900) % 400));
 140         yrs = 72;
 141
 142         /*
 143          * We want to keep the year set to 73 until March
 144          * for non-leap years, so that Feb, 29th is handled
 145          * correctly.
 146          */
 147         if (!leap_yr && mon < 3) {
 148                 real_yrs--;
 149                 yrs = 73;
 150         }
 151 #endif
 152
 153 #ifdef CONFIG_ACPI
 154         if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
 155             acpi_gbl_FADT.century) {
 156                 century = (yrs + 1900) / 100;
 157                 yrs %= 100;
 158         }
 159 #endif
 160
 161         /* These limits and adjustments are independent of
 162          * whether the chip is in binary mode or not.
 163          */
 164         if (yrs > 169) {
 165                 spin_unlock_irqrestore(&rtc_lock, flags);
 166                 return -EINVAL;
 167         }
 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         save_control = CMOS_READ(RTC_CONTROL);
 184         CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
 185         save_freq_select = CMOS_READ(RTC_FREQ_SELECT);
 186         if (apply_amd_register_a_behavior())
 187                 CMOS_WRITE((save_freq_select & ~RTC_AMD_BANK_SELECT), RTC_FREQ_SELECT);
 188         else
 189                 CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);
 190
 191 #ifdef CONFIG_MACH_DECSTATION
 192         CMOS_WRITE(real_yrs, RTC_DEC_YEAR);
 193 #endif
 194         CMOS_WRITE(yrs, RTC_YEAR);
 195         CMOS_WRITE(mon, RTC_MONTH);
 196         CMOS_WRITE(day, RTC_DAY_OF_MONTH);
 197         CMOS_WRITE(hrs, RTC_HOURS);
 198         CMOS_WRITE(min, RTC_MINUTES);
 199         CMOS_WRITE(sec, RTC_SECONDS);
 200 #ifdef CONFIG_ACPI
 201         if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
 202             acpi_gbl_FADT.century)
 203                 CMOS_WRITE(century, acpi_gbl_FADT.century);
 204 #endif
 205
 206         CMOS_WRITE(save_control, RTC_CONTROL);
 207         CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
 208
 209         spin_unlock_irqrestore(&rtc_lock, flags);
 210
 211         return 0;
 212 }
 213 EXPORT_SYMBOL_GPL(mc146818_set_time);