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  * Execute a function while the UIP (Update-in-progress) bit of the RTC is
  13  * unset.
  14  *
  15  * Warning: callback may be executed more then once.
  16  */
  17 bool mc146818_avoid_UIP(void (*callback)(unsigned char seconds, void *param),
  18                         void *param)
  19 {
  20         int i;
  21         unsigned long flags;
  22         unsigned char seconds;
  23
  24         for (i = 0; i < 100; i++) {
  25                 spin_lock_irqsave(&rtc_lock, flags);
  26
  27                 /*
  28                  * Check whether there is an update in progress during which the
  29                  * readout is unspecified. The maximum update time is ~2ms. Poll
  30                  * every 100 usec for completion.
  31                  *
  32                  * Store the second value before checking UIP so a long lasting
  33                  * NMI which happens to hit after the UIP check cannot make
  34                  * an update cycle invisible.
  35                  */
  36                 seconds = CMOS_READ(RTC_SECONDS);
  37
  38                 if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) {
  39                         spin_unlock_irqrestore(&rtc_lock, flags);
  40                         udelay(100);
  41                         continue;
  42                 }
  43
  44                 /* Revalidate the above readout */
  45                 if (seconds != CMOS_READ(RTC_SECONDS)) {
  46                         spin_unlock_irqrestore(&rtc_lock, flags);
  47                         continue;
  48                 }
  49
  50                 if (callback)
  51                         callback(seconds, param);
  52
  53                 /*
  54                  * Check for the UIP bit again. If it is set now then
  55                  * the above values may contain garbage.
  56                  */
  57                 if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) {
  58                         spin_unlock_irqrestore(&rtc_lock, flags);
  59                         udelay(100);
  60                         continue;
  61                 }
  62
  63                 /*
  64                  * A NMI might have interrupted the above sequence so check
  65                  * whether the seconds value has changed which indicates that
  66                  * the NMI took longer than the UIP bit was set. Unlikely, but
  67                  * possible and there is also virt...
  68                  */
  69                 if (seconds != CMOS_READ(RTC_SECONDS)) {
  70                         spin_unlock_irqrestore(&rtc_lock, flags);
  71                         continue;
  72                 }
  73                 spin_unlock_irqrestore(&rtc_lock, flags);
  74
  75                 return true;
  76         }
  77         return false;
  78 }
  79 EXPORT_SYMBOL_GPL(mc146818_avoid_UIP);
  80
  81 /*
  82  * If the UIP (Update-in-progress) bit of the RTC is set for more then
  83  * 10ms, the RTC is apparently broken or not present.
  84  */
  85 bool mc146818_does_rtc_work(void)
  86 {
  87         return mc146818_avoid_UIP(NULL, NULL);
  88 }
  89 EXPORT_SYMBOL_GPL(mc146818_does_rtc_work);
  90
  91 struct mc146818_get_time_callback_param {
  92         struct rtc_time *time;
  93         unsigned char ctrl;
  94 #ifdef CONFIG_ACPI
  95         unsigned char century;
  96 #endif
  97 #ifdef CONFIG_MACH_DECSTATION
  98         unsigned int real_year;
  99 #endif
 100 };
 101
 102 static void mc146818_get_time_callback(unsigned char seconds, void *param_in)
 103 {
 104         struct mc146818_get_time_callback_param *p = param_in;
 105
 106         /*
 107          * Only the values that we read from the RTC are set. We leave
 108          * tm_wday, tm_yday and tm_isdst untouched. Even though the
 109          * RTC has RTC_DAY_OF_WEEK, we ignore it, as it is only updated
 110          * by the RTC when initially set to a non-zero value.
 111          */
 112         p->time->tm_sec = seconds;
 113         p->time->tm_min = CMOS_READ(RTC_MINUTES);
 114         p->time->tm_hour = CMOS_READ(RTC_HOURS);
 115         p->time->tm_mday = CMOS_READ(RTC_DAY_OF_MONTH);
 116         p->time->tm_mon = CMOS_READ(RTC_MONTH);
 117         p->time->tm_year = CMOS_READ(RTC_YEAR);
 118 #ifdef CONFIG_MACH_DECSTATION
 119         p->real_year = CMOS_READ(RTC_DEC_YEAR);
 120 #endif
 121 #ifdef CONFIG_ACPI
 122         if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
 123             acpi_gbl_FADT.century) {
 124                 p->century = CMOS_READ(acpi_gbl_FADT.century);
 125         } else {
 126                 p->century = 0;
 127         }
 128 #endif
 129
 130         p->ctrl = CMOS_READ(RTC_CONTROL);
 131 }
 132
 133 int mc146818_get_time(struct rtc_time *time)
 134 {
 135         struct mc146818_get_time_callback_param p = {
 136                 .time = time
 137         };
 138
 139         if (!mc146818_avoid_UIP(mc146818_get_time_callback, &p)) {
 140                 memset(time, 0, sizeof(*time));
 141                 return -EIO;
 142         }
 143
 144         if (!(p.ctrl & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
 145         {
 146                 time->tm_sec = bcd2bin(time->tm_sec);
 147                 time->tm_min = bcd2bin(time->tm_min);
 148                 time->tm_hour = bcd2bin(time->tm_hour);
 149                 time->tm_mday = bcd2bin(time->tm_mday);
 150                 time->tm_mon = bcd2bin(time->tm_mon);
 151                 time->tm_year = bcd2bin(time->tm_year);
 152 #ifdef CONFIG_ACPI
 153                 p.century = bcd2bin(p.century);
 154 #endif
 155         }
 156
 157 #ifdef CONFIG_MACH_DECSTATION
 158         time->tm_year += p.real_year - 72;
 159 #endif
 160
 161 #ifdef CONFIG_ACPI
 162         if (p.century > 19)
 163                 time->tm_year += (p.century - 19) * 100;
 164 #endif
 165
 166         /*
 167          * Account for differences between how the RTC uses the values
 168          * and how they are defined in a struct rtc_time;
 169          */
 170         if (time->tm_year <= 69)
 171                 time->tm_year += 100;
 172
 173         time->tm_mon--;
 174
 175         return 0;
 176 }
 177 EXPORT_SYMBOL_GPL(mc146818_get_time);
 178
 179 /* AMD systems don't allow access to AltCentury with DV1 */
 180 static bool apply_amd_register_a_behavior(void)
 181 {
 182 #ifdef CONFIG_X86
 183         if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
 184             boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
 185                 return true;
 186 #endif
 187         return false;
 188 }
 189
 190 /* Set the current date and time in the real time clock. */
 191 int mc146818_set_time(struct rtc_time *time)
 192 {
 193         unsigned long flags;
 194         unsigned char mon, day, hrs, min, sec;
 195         unsigned char save_control, save_freq_select;
 196         unsigned int yrs;
 197 #ifdef CONFIG_MACH_DECSTATION
 198         unsigned int real_yrs, leap_yr;
 199 #endif
 200         unsigned char century = 0;
 201
 202         yrs = time->tm_year;
 203         mon = time->tm_mon + 1;   /* tm_mon starts at zero */
 204         day = time->tm_mday;
 205         hrs = time->tm_hour;
 206         min = time->tm_min;
 207         sec = time->tm_sec;
 208
 209         if (yrs > 255)  /* They are unsigned */
 210                 return -EINVAL;
 211
 212 #ifdef CONFIG_MACH_DECSTATION
 213         real_yrs = yrs;
 214         leap_yr = ((!((yrs + 1900) % 4) && ((yrs + 1900) % 100)) ||
 215                         !((yrs + 1900) % 400));
 216         yrs = 72;
 217
 218         /*
 219          * We want to keep the year set to 73 until March
 220          * for non-leap years, so that Feb, 29th is handled
 221          * correctly.
 222          */
 223         if (!leap_yr && mon < 3) {
 224                 real_yrs--;
 225                 yrs = 73;
 226         }
 227 #endif
 228
 229 #ifdef CONFIG_ACPI
 230         if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
 231             acpi_gbl_FADT.century) {
 232                 century = (yrs + 1900) / 100;
 233                 yrs %= 100;
 234         }
 235 #endif
 236
 237         /* These limits and adjustments are independent of
 238          * whether the chip is in binary mode or not.
 239          */
 240         if (yrs > 169)
 241                 return -EINVAL;
 242
 243         if (yrs >= 100)
 244                 yrs -= 100;
 245
 246         spin_lock_irqsave(&rtc_lock, flags);
 247         save_control = CMOS_READ(RTC_CONTROL);
 248         spin_unlock_irqrestore(&rtc_lock, flags);
 249         if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
 250                 sec = bin2bcd(sec);
 251                 min = bin2bcd(min);
 252                 hrs = bin2bcd(hrs);
 253                 day = bin2bcd(day);
 254                 mon = bin2bcd(mon);
 255                 yrs = bin2bcd(yrs);
 256                 century = bin2bcd(century);
 257         }
 258
 259         spin_lock_irqsave(&rtc_lock, flags);
 260         save_control = CMOS_READ(RTC_CONTROL);
 261         CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
 262         save_freq_select = CMOS_READ(RTC_FREQ_SELECT);
 263         if (apply_amd_register_a_behavior())
 264                 CMOS_WRITE((save_freq_select & ~RTC_AMD_BANK_SELECT), RTC_FREQ_SELECT);
 265         else
 266                 CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);
 267
 268 #ifdef CONFIG_MACH_DECSTATION
 269         CMOS_WRITE(real_yrs, RTC_DEC_YEAR);
 270 #endif
 271         CMOS_WRITE(yrs, RTC_YEAR);
 272         CMOS_WRITE(mon, RTC_MONTH);
 273         CMOS_WRITE(day, RTC_DAY_OF_MONTH);
 274         CMOS_WRITE(hrs, RTC_HOURS);
 275         CMOS_WRITE(min, RTC_MINUTES);
 276         CMOS_WRITE(sec, RTC_SECONDS);
 277 #ifdef CONFIG_ACPI
 278         if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
 279             acpi_gbl_FADT.century)
 280                 CMOS_WRITE(century, acpi_gbl_FADT.century);
 281 #endif
 282
 283         CMOS_WRITE(save_control, RTC_CONTROL);
 284         CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
 285
 286         spin_unlock_irqrestore(&rtc_lock, flags);
 287
 288         return 0;
 289 }
 290 EXPORT_SYMBOL_GPL(mc146818_set_time);