/* * RTC subsystem, initialize system time on startup * * Copyright (C) 2005 Tower Technologies * Author: Alessandro Zummo <a.zummo@towertech.it> * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2 as * published by the Free Software Foundation. */ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include <linux/rtc.h> /* IMPORTANT: the RTC only stores whole seconds. It is arbitrary * whether it stores the most close value or the value with partial * seconds truncated. However, it is important that we use it to store * the truncated value. This is because otherwise it is necessary, * in an rtc sync function, to read both xtime.tv_sec and * xtime.tv_nsec. On some processors (i.e. ARM), an atomic read * of >32bits is not possible. So storing the most close value would * slow down the sync API. So here we have the truncated value and * the best guess is to add 0.5s. */ static int __init rtc_hctosys(void) { int err = -ENODEV; struct rtc_time tm; struct timespec64 tv64 = { .tv_nsec = NSEC_PER_SEC >> 1, }; struct rtc_device *rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE); if (rtc == NULL) { pr_info("unable to open rtc device (%s)\n", CONFIG_RTC_HCTOSYS_DEVICE); goto err_open; } err = rtc_read_time(rtc, &tm); if (err) { dev_err(rtc->dev.parent, "hctosys: unable to read the hardware clock\n"); goto err_read; } tv64.tv_sec = rtc_tm_to_time64(&tm); #if BITS_PER_LONG == 32 if (tv64.tv_sec > INT_MAX) goto err_read; #endif err = do_settimeofday64(&tv64); dev_info(rtc->dev.parent, "setting system clock to " "%d-%02d-%02d %02d:%02d:%02d UTC (%lld)\n", tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday, tm.tm_hour, tm.tm_min, tm.tm_sec, (long long) tv64.tv_sec); err_read: rtc_class_close(rtc); err_open: rtc_hctosys_ret = err; return err; } late_initcall(rtc_hctosys);