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  * If the UIP (Update-in-progress) bit of the RTC is set for more then
  13  * 10ms, the RTC is apparently broken or not present.
  14  */
  15 bool mc146818_does_rtc_work(void)
  16 {
  17         int i;
  18         unsigned char val;
  19         unsigned long flags;
  20
  21         for (i = 0; i < 10; i++) {
  22                 spin_lock_irqsave(&rtc_lock, flags);
  23                 val = CMOS_READ(RTC_FREQ_SELECT);
  24                 spin_unlock_irqrestore(&rtc_lock, flags);
  25
  26                 if ((val & RTC_UIP) == 0)
  27                         return true;
  28
  29                 mdelay(1);
  30         }
  31
  32         return false;
  33 }
  34 EXPORT_SYMBOL_GPL(mc146818_does_rtc_work);
  35
  36 int mc146818_get_time(struct rtc_time *time)
  37 {
  38         unsigned char ctrl;
  39         unsigned long flags;
  40         unsigned int iter_count = 0;
  41         unsigned char century = 0;
  42         bool retry;
  43
  44 #ifdef CONFIG_MACH_DECSTATION
  45         unsigned int real_year;
  46 #endif
  47
  48 again:
  49         if (iter_count > 10) {
  50                 memset(time, 0, sizeof(*time));
  51                 return -EIO;
  52         }
  53         iter_count++;
  54
  55         spin_lock_irqsave(&rtc_lock, flags);
  56
  57         /*
  58          * Check whether there is an update in progress during which the
  59          * readout is unspecified. The maximum update time is ~2ms. Poll
  60          * every msec for completion.
  61          *
  62          * Store the second value before checking UIP so a long lasting NMI
  63          * which happens to hit after the UIP check cannot make an update
  64          * cycle invisible.
  65          */
  66         time->tm_sec = CMOS_READ(RTC_SECONDS);
  67
  68         if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) {
  69                 spin_unlock_irqrestore(&rtc_lock, flags);
  70                 mdelay(1);
  71                 goto again;
  72         }
  73
  74         /* Revalidate the above readout */
  75         if (time->tm_sec != CMOS_READ(RTC_SECONDS)) {
  76                 spin_unlock_irqrestore(&rtc_lock, flags);
  77                 goto again;
  78         }
  79
  80         /*
  81          * Only the values that we read from the RTC are set. We leave
  82          * tm_wday, tm_yday and tm_isdst untouched. Even though the
  83          * RTC has RTC_DAY_OF_WEEK, we ignore it, as it is only updated
  84          * by the RTC when initially set to a non-zero value.
  85          */
  86         time->tm_min = CMOS_READ(RTC_MINUTES);
  87         time->tm_hour = CMOS_READ(RTC_HOURS);
  88         time->tm_mday = CMOS_READ(RTC_DAY_OF_MONTH);
  89         time->tm_mon = CMOS_READ(RTC_MONTH);
  90         time->tm_year = CMOS_READ(RTC_YEAR);
  91 #ifdef CONFIG_MACH_DECSTATION
  92         real_year = CMOS_READ(RTC_DEC_YEAR);
  93 #endif
  94 #ifdef CONFIG_ACPI
  95         if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
  96             acpi_gbl_FADT.century)
  97                 century = CMOS_READ(acpi_gbl_FADT.century);
  98 #endif
  99         ctrl = CMOS_READ(RTC_CONTROL);
 100         /*
 101          * Check for the UIP bit again. If it is set now then
 102          * the above values may contain garbage.
 103          */
 104         retry = CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP;
 105         /*
 106          * A NMI might have interrupted the above sequence so check whether
 107          * the seconds value has changed which indicates that the NMI took
 108          * longer than the UIP bit was set. Unlikely, but possible and
 109          * there is also virt...
 110          */
 111         retry |= time->tm_sec != CMOS_READ(RTC_SECONDS);
 112
 113         spin_unlock_irqrestore(&rtc_lock, flags);
 114
 115         if (retry)
 116                 goto again;
 117
 118         if (!(ctrl & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
 119         {
 120                 time->tm_sec = bcd2bin(time->tm_sec);
 121                 time->tm_min = bcd2bin(time->tm_min);
 122                 time->tm_hour = bcd2bin(time->tm_hour);
 123                 time->tm_mday = bcd2bin(time->tm_mday);
 124                 time->tm_mon = bcd2bin(time->tm_mon);
 125                 time->tm_year = bcd2bin(time->tm_year);
 126                 century = bcd2bin(century);
 127         }
 128
 129 #ifdef CONFIG_MACH_DECSTATION
 130         time->tm_year += real_year - 72;
 131 #endif
 132
 133         if (century > 19)
 134                 time->tm_year += (century - 19) * 100;
 135
 136         /*
 137          * Account for differences between how the RTC uses the values
 138          * and how they are defined in a struct rtc_time;
 139          */
 140         if (time->tm_year <= 69)
 141                 time->tm_year += 100;
 142
 143         time->tm_mon--;
 144
 145         return 0;
 146 }
 147 EXPORT_SYMBOL_GPL(mc146818_get_time);
 148
 149 /* AMD systems don't allow access to AltCentury with DV1 */
 150 static bool apply_amd_register_a_behavior(void)
 151 {
 152 #ifdef CONFIG_X86
 153         if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
 154             boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
 155                 return true;
 156 #endif
 157         return false;
 158 }
 159
 160 /* Set the current date and time in the real time clock. */
 161 int mc146818_set_time(struct rtc_time *time)
 162 {
 163         unsigned long flags;
 164         unsigned char mon, day, hrs, min, sec;
 165         unsigned char save_control, save_freq_select;
 166         unsigned int yrs;
 167 #ifdef CONFIG_MACH_DECSTATION
 168         unsigned int real_yrs, leap_yr;
 169 #endif
 170         unsigned char century = 0;
 171
 172         yrs = time->tm_year;
 173         mon = time->tm_mon + 1;   /* tm_mon starts at zero */
 174         day = time->tm_mday;
 175         hrs = time->tm_hour;
 176         min = time->tm_min;
 177         sec = time->tm_sec;
 178
 179         if (yrs > 255)  /* They are unsigned */
 180                 return -EINVAL;
 181
 182 #ifdef CONFIG_MACH_DECSTATION
 183         real_yrs = yrs;
 184         leap_yr = ((!((yrs + 1900) % 4) && ((yrs + 1900) % 100)) ||
 185                         !((yrs + 1900) % 400));
 186         yrs = 72;
 187
 188         /*
 189          * We want to keep the year set to 73 until March
 190          * for non-leap years, so that Feb, 29th is handled
 191          * correctly.
 192          */
 193         if (!leap_yr && mon < 3) {
 194                 real_yrs--;
 195                 yrs = 73;
 196         }
 197 #endif
 198
 199 #ifdef CONFIG_ACPI
 200         if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
 201             acpi_gbl_FADT.century) {
 202                 century = (yrs + 1900) / 100;
 203                 yrs %= 100;
 204         }
 205 #endif
 206
 207         /* These limits and adjustments are independent of
 208          * whether the chip is in binary mode or not.
 209          */
 210         if (yrs > 169)
 211                 return -EINVAL;
 212
 213         if (yrs >= 100)
 214                 yrs -= 100;
 215
 216         spin_lock_irqsave(&rtc_lock, flags);
 217         save_control = CMOS_READ(RTC_CONTROL);
 218         spin_unlock_irqrestore(&rtc_lock, flags);
 219         if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
 220                 sec = bin2bcd(sec);
 221                 min = bin2bcd(min);
 222                 hrs = bin2bcd(hrs);
 223                 day = bin2bcd(day);
 224                 mon = bin2bcd(mon);
 225                 yrs = bin2bcd(yrs);
 226                 century = bin2bcd(century);
 227         }
 228
 229         spin_lock_irqsave(&rtc_lock, flags);
 230         save_control = CMOS_READ(RTC_CONTROL);
 231         CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
 232         save_freq_select = CMOS_READ(RTC_FREQ_SELECT);
 233         if (apply_amd_register_a_behavior())
 234                 CMOS_WRITE((save_freq_select & ~RTC_AMD_BANK_SELECT), RTC_FREQ_SELECT);
 235         else
 236                 CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);
 237
 238 #ifdef CONFIG_MACH_DECSTATION
 239         CMOS_WRITE(real_yrs, RTC_DEC_YEAR);
 240 #endif
 241         CMOS_WRITE(yrs, RTC_YEAR);
 242         CMOS_WRITE(mon, RTC_MONTH);
 243         CMOS_WRITE(day, RTC_DAY_OF_MONTH);
 244         CMOS_WRITE(hrs, RTC_HOURS);
 245         CMOS_WRITE(min, RTC_MINUTES);
 246         CMOS_WRITE(sec, RTC_SECONDS);
 247 #ifdef CONFIG_ACPI
 248         if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
 249             acpi_gbl_FADT.century)
 250                 CMOS_WRITE(century, acpi_gbl_FADT.century);
 251 #endif
 252
 253         CMOS_WRITE(save_control, RTC_CONTROL);
 254         CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
 255
 256         spin_unlock_irqrestore(&rtc_lock, flags);
 257
 258         return 0;
 259 }
 260 EXPORT_SYMBOL_GPL(mc146818_set_time);