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 #define UIP_RECHECK_DELAY               100     /* usec */
  12 #define UIP_RECHECK_DELAY_MS            (USEC_PER_MSEC / UIP_RECHECK_DELAY)
  13 #define UIP_RECHECK_LOOPS_MS(x)         (x / UIP_RECHECK_DELAY_MS)
  14
  15 /*
  16  * Execute a function while the UIP (Update-in-progress) bit of the RTC is
  17  * unset. The timeout is configurable by the caller in ms.
  18  *
  19  * Warning: callback may be executed more then once.
  20  */
  21 bool mc146818_avoid_UIP(void (*callback)(unsigned char seconds, void *param),
  22                         int timeout,
  23                         void *param)
  24 {
  25         int i;
  26         unsigned long flags;
  27         unsigned char seconds;
  28
  29         for (i = 0; UIP_RECHECK_LOOPS_MS(i) < timeout; i++) {
  30                 spin_lock_irqsave(&rtc_lock, flags);
  31
  32                 /*
  33                  * Check whether there is an update in progress during which the
  34                  * readout is unspecified. The maximum update time is ~2ms. Poll
  35                  * for completion.
  36                  *
  37                  * Store the second value before checking UIP so a long lasting
  38                  * NMI which happens to hit after the UIP check cannot make
  39                  * an update cycle invisible.
  40                  */
  41                 seconds = CMOS_READ(RTC_SECONDS);
  42
  43                 if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) {
  44                         spin_unlock_irqrestore(&rtc_lock, flags);
  45                         udelay(UIP_RECHECK_DELAY);
  46                         continue;
  47                 }
  48
  49                 /* Revalidate the above readout */
  50                 if (seconds != CMOS_READ(RTC_SECONDS)) {
  51                         spin_unlock_irqrestore(&rtc_lock, flags);
  52                         continue;
  53                 }
  54
  55                 if (callback)
  56                         callback(seconds, param);
  57
  58                 /*
  59                  * Check for the UIP bit again. If it is set now then
  60                  * the above values may contain garbage.
  61                  */
  62                 if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) {
  63                         spin_unlock_irqrestore(&rtc_lock, flags);
  64                         udelay(UIP_RECHECK_DELAY);
  65                         continue;
  66                 }
  67
  68                 /*
  69                  * A NMI might have interrupted the above sequence so check
  70                  * whether the seconds value has changed which indicates that
  71                  * the NMI took longer than the UIP bit was set. Unlikely, but
  72                  * possible and there is also virt...
  73                  */
  74                 if (seconds != CMOS_READ(RTC_SECONDS)) {
  75                         spin_unlock_irqrestore(&rtc_lock, flags);
  76                         continue;
  77                 }
  78                 spin_unlock_irqrestore(&rtc_lock, flags);
  79
  80                 if (UIP_RECHECK_LOOPS_MS(i) >= 100)
  81                         pr_warn("Reading current time from RTC took around %li ms\n",
  82                                 UIP_RECHECK_LOOPS_MS(i));
  83
  84                 return true;
  85         }
  86         return false;
  87 }
  88 EXPORT_SYMBOL_GPL(mc146818_avoid_UIP);
  89
  90 /*
  91  * If the UIP (Update-in-progress) bit of the RTC is set for more then
  92  * 10ms, the RTC is apparently broken or not present.
  93  */
  94 bool mc146818_does_rtc_work(void)
  95 {
  96         return mc146818_avoid_UIP(NULL, 1000, NULL);
  97 }
  98 EXPORT_SYMBOL_GPL(mc146818_does_rtc_work);
  99
 100 struct mc146818_get_time_callback_param {
 101         struct rtc_time *time;
 102         unsigned char ctrl;
 103 #ifdef CONFIG_ACPI
 104         unsigned char century;
 105 #endif
 106 #ifdef CONFIG_MACH_DECSTATION
 107         unsigned int real_year;
 108 #endif
 109 };
 110
 111 static void mc146818_get_time_callback(unsigned char seconds, void *param_in)
 112 {
 113         struct mc146818_get_time_callback_param *p = param_in;
 114
 115         /*
 116          * Only the values that we read from the RTC are set. We leave
 117          * tm_wday, tm_yday and tm_isdst untouched. Even though the
 118          * RTC has RTC_DAY_OF_WEEK, we ignore it, as it is only updated
 119          * by the RTC when initially set to a non-zero value.
 120          */
 121         p->time->tm_sec = seconds;
 122         p->time->tm_min = CMOS_READ(RTC_MINUTES);
 123         p->time->tm_hour = CMOS_READ(RTC_HOURS);
 124         p->time->tm_mday = CMOS_READ(RTC_DAY_OF_MONTH);
 125         p->time->tm_mon = CMOS_READ(RTC_MONTH);
 126         p->time->tm_year = CMOS_READ(RTC_YEAR);
 127 #ifdef CONFIG_MACH_DECSTATION
 128         p->real_year = CMOS_READ(RTC_DEC_YEAR);
 129 #endif
 130 #ifdef CONFIG_ACPI
 131         if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
 132             acpi_gbl_FADT.century) {
 133                 p->century = CMOS_READ(acpi_gbl_FADT.century);
 134         } else {
 135                 p->century = 0;
 136         }
 137 #endif
 138
 139         p->ctrl = CMOS_READ(RTC_CONTROL);
 140 }
 141
 142 /**
 143  * mc146818_get_time - Get the current time from the RTC
 144  * @time: pointer to struct rtc_time to store the current time
 145  * @timeout: timeout value in ms
 146  *
 147  * This function reads the current time from the RTC and stores it in the
 148  * provided struct rtc_time. The timeout parameter specifies the maximum
 149  * time to wait for the RTC to become ready.
 150  *
 151  * Return: 0 on success, -ETIMEDOUT if the RTC did not become ready within
 152  * the specified timeout, or another error code if an error occurred.
 153  */
 154 int mc146818_get_time(struct rtc_time *time, int timeout)
 155 {
 156         struct mc146818_get_time_callback_param p = {
 157                 .time = time
 158         };
 159
 160         if (!mc146818_avoid_UIP(mc146818_get_time_callback, timeout, &p)) {
 161                 memset(time, 0, sizeof(*time));
 162                 return -ETIMEDOUT;
 163         }
 164
 165         if (!(p.ctrl & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
 166         {
 167                 time->tm_sec = bcd2bin(time->tm_sec);
 168                 time->tm_min = bcd2bin(time->tm_min);
 169                 time->tm_hour = bcd2bin(time->tm_hour);
 170                 time->tm_mday = bcd2bin(time->tm_mday);
 171                 time->tm_mon = bcd2bin(time->tm_mon);
 172                 time->tm_year = bcd2bin(time->tm_year);
 173 #ifdef CONFIG_ACPI
 174                 p.century = bcd2bin(p.century);
 175 #endif
 176         }
 177
 178 #ifdef CONFIG_MACH_DECSTATION
 179         time->tm_year += p.real_year - 72;
 180 #endif
 181
 182 #ifdef CONFIG_ACPI
 183         if (p.century > 19)
 184                 time->tm_year += (p.century - 19) * 100;
 185 #endif
 186
 187         /*
 188          * Account for differences between how the RTC uses the values
 189          * and how they are defined in a struct rtc_time;
 190          */
 191         if (time->tm_year <= 69)
 192                 time->tm_year += 100;
 193
 194         time->tm_mon--;
 195
 196         return 0;
 197 }
 198 EXPORT_SYMBOL_GPL(mc146818_get_time);
 199
 200 /* AMD systems don't allow access to AltCentury with DV1 */
 201 static bool apply_amd_register_a_behavior(void)
 202 {
 203 #ifdef CONFIG_X86
 204         if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
 205             boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
 206                 return true;
 207 #endif
 208         return false;
 209 }
 210
 211 /* Set the current date and time in the real time clock. */
 212 int mc146818_set_time(struct rtc_time *time)
 213 {
 214         unsigned long flags;
 215         unsigned char mon, day, hrs, min, sec;
 216         unsigned char save_control, save_freq_select;
 217         unsigned int yrs;
 218 #ifdef CONFIG_MACH_DECSTATION
 219         unsigned int real_yrs, leap_yr;
 220 #endif
 221         unsigned char century = 0;
 222
 223         yrs = time->tm_year;
 224         mon = time->tm_mon + 1;   /* tm_mon starts at zero */
 225         day = time->tm_mday;
 226         hrs = time->tm_hour;
 227         min = time->tm_min;
 228         sec = time->tm_sec;
 229
 230         if (yrs > 255)  /* They are unsigned */
 231                 return -EINVAL;
 232
 233 #ifdef CONFIG_MACH_DECSTATION
 234         real_yrs = yrs;
 235         leap_yr = ((!((yrs + 1900) % 4) && ((yrs + 1900) % 100)) ||
 236                         !((yrs + 1900) % 400));
 237         yrs = 72;
 238
 239         /*
 240          * We want to keep the year set to 73 until March
 241          * for non-leap years, so that Feb, 29th is handled
 242          * correctly.
 243          */
 244         if (!leap_yr && mon < 3) {
 245                 real_yrs--;
 246                 yrs = 73;
 247         }
 248 #endif
 249
 250 #ifdef CONFIG_ACPI
 251         if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
 252             acpi_gbl_FADT.century) {
 253                 century = (yrs + 1900) / 100;
 254                 yrs %= 100;
 255         }
 256 #endif
 257
 258         /* These limits and adjustments are independent of
 259          * whether the chip is in binary mode or not.
 260          */
 261         if (yrs > 169)
 262                 return -EINVAL;
 263
 264         if (yrs >= 100)
 265                 yrs -= 100;
 266
 267         spin_lock_irqsave(&rtc_lock, flags);
 268         save_control = CMOS_READ(RTC_CONTROL);
 269         spin_unlock_irqrestore(&rtc_lock, flags);
 270         if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
 271                 sec = bin2bcd(sec);
 272                 min = bin2bcd(min);
 273                 hrs = bin2bcd(hrs);
 274                 day = bin2bcd(day);
 275                 mon = bin2bcd(mon);
 276                 yrs = bin2bcd(yrs);
 277                 century = bin2bcd(century);
 278         }
 279
 280         spin_lock_irqsave(&rtc_lock, flags);
 281         save_control = CMOS_READ(RTC_CONTROL);
 282         CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
 283         save_freq_select = CMOS_READ(RTC_FREQ_SELECT);
 284         if (apply_amd_register_a_behavior())
 285                 CMOS_WRITE((save_freq_select & ~RTC_AMD_BANK_SELECT), RTC_FREQ_SELECT);
 286         else
 287                 CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);
 288
 289 #ifdef CONFIG_MACH_DECSTATION
 290         CMOS_WRITE(real_yrs, RTC_DEC_YEAR);
 291 #endif
 292         CMOS_WRITE(yrs, RTC_YEAR);
 293         CMOS_WRITE(mon, RTC_MONTH);
 294         CMOS_WRITE(day, RTC_DAY_OF_MONTH);
 295         CMOS_WRITE(hrs, RTC_HOURS);
 296         CMOS_WRITE(min, RTC_MINUTES);
 297         CMOS_WRITE(sec, RTC_SECONDS);
 298 #ifdef CONFIG_ACPI
 299         if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
 300             acpi_gbl_FADT.century)
 301                 CMOS_WRITE(century, acpi_gbl_FADT.century);
 302 #endif
 303
 304         CMOS_WRITE(save_control, RTC_CONTROL);
 305         CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
 306
 307         spin_unlock_irqrestore(&rtc_lock, flags);
 308
 309         return 0;
 310 }
 311 EXPORT_SYMBOL_GPL(mc146818_set_time);