1 // SPDX-License-Identifier: GPL-2.0-only
3 #include <linux/delay.h>
4 #include <linux/export.h>
5 #include <linux/mc146818rtc.h>
8 #include <linux/acpi.h>
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)
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.
19 * Warning: callback may be executed more then once.
21 bool mc146818_avoid_UIP(void (*callback)(unsigned char seconds, void *param),
27 unsigned char seconds;
29 for (i = 0; UIP_RECHECK_LOOPS_MS(i) < timeout; i++) {
30 spin_lock_irqsave(&rtc_lock, flags);
33 * Check whether there is an update in progress during which the
34 * readout is unspecified. The maximum update time is ~2ms. Poll
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.
41 seconds = CMOS_READ(RTC_SECONDS);
43 if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) {
44 spin_unlock_irqrestore(&rtc_lock, flags);
45 udelay(UIP_RECHECK_DELAY);
49 /* Revalidate the above readout */
50 if (seconds != CMOS_READ(RTC_SECONDS)) {
51 spin_unlock_irqrestore(&rtc_lock, flags);
56 callback(seconds, param);
59 * Check for the UIP bit again. If it is set now then
60 * the above values may contain garbage.
62 if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) {
63 spin_unlock_irqrestore(&rtc_lock, flags);
64 udelay(UIP_RECHECK_DELAY);
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...
74 if (seconds != CMOS_READ(RTC_SECONDS)) {
75 spin_unlock_irqrestore(&rtc_lock, flags);
78 spin_unlock_irqrestore(&rtc_lock, flags);
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));
88 EXPORT_SYMBOL_GPL(mc146818_avoid_UIP);
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.
94 bool mc146818_does_rtc_work(void)
96 return mc146818_avoid_UIP(NULL, 1000, NULL);
98 EXPORT_SYMBOL_GPL(mc146818_does_rtc_work);
100 struct mc146818_get_time_callback_param {
101 struct rtc_time *time;
104 unsigned char century;
106 #ifdef CONFIG_MACH_DECSTATION
107 unsigned int real_year;
111 static void mc146818_get_time_callback(unsigned char seconds, void *param_in)
113 struct mc146818_get_time_callback_param *p = param_in;
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.
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);
131 if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
132 acpi_gbl_FADT.century) {
133 p->century = CMOS_READ(acpi_gbl_FADT.century);
139 p->ctrl = CMOS_READ(RTC_CONTROL);
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
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.
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.
154 int mc146818_get_time(struct rtc_time *time, int timeout)
156 struct mc146818_get_time_callback_param p = {
160 if (!mc146818_avoid_UIP(mc146818_get_time_callback, timeout, &p)) {
161 memset(time, 0, sizeof(*time));
165 if (!(p.ctrl & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
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);
174 p.century = bcd2bin(p.century);
178 #ifdef CONFIG_MACH_DECSTATION
179 time->tm_year += p.real_year - 72;
184 time->tm_year += (p.century - 19) * 100;
188 * Account for differences between how the RTC uses the values
189 * and how they are defined in a struct rtc_time;
191 if (time->tm_year <= 69)
192 time->tm_year += 100;
198 EXPORT_SYMBOL_GPL(mc146818_get_time);
200 /* AMD systems don't allow access to AltCentury with DV1 */
201 static bool apply_amd_register_a_behavior(void)
204 if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
205 boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
211 /* Set the current date and time in the real time clock. */
212 int mc146818_set_time(struct rtc_time *time)
215 unsigned char mon, day, hrs, min, sec;
216 unsigned char save_control, save_freq_select;
218 #ifdef CONFIG_MACH_DECSTATION
219 unsigned int real_yrs, leap_yr;
221 unsigned char century = 0;
224 mon = time->tm_mon + 1; /* tm_mon starts at zero */
230 if (yrs > 255) /* They are unsigned */
233 #ifdef CONFIG_MACH_DECSTATION
235 leap_yr = ((!((yrs + 1900) % 4) && ((yrs + 1900) % 100)) ||
236 !((yrs + 1900) % 400));
240 * We want to keep the year set to 73 until March
241 * for non-leap years, so that Feb, 29th is handled
244 if (!leap_yr && mon < 3) {
251 if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
252 acpi_gbl_FADT.century) {
253 century = (yrs + 1900) / 100;
258 /* These limits and adjustments are independent of
259 * whether the chip is in binary mode or not.
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) {
277 century = bin2bcd(century);
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);
287 CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);
289 #ifdef CONFIG_MACH_DECSTATION
290 CMOS_WRITE(real_yrs, RTC_DEC_YEAR);
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);
299 if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
300 acpi_gbl_FADT.century)
301 CMOS_WRITE(century, acpi_gbl_FADT.century);
304 CMOS_WRITE(save_control, RTC_CONTROL);
305 CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
307 spin_unlock_irqrestore(&rtc_lock, flags);
311 EXPORT_SYMBOL_GPL(mc146818_set_time);