| 1 | /* |
| 2 | * RTC subsystem, initialize system time on startup |
| 3 | * |
| 4 | * Copyright (C) 2005 Tower Technologies |
| 5 | * Author: Alessandro Zummo <a.zummo@towertech.it> |
| 6 | * |
| 7 | * This program is free software; you can redistribute it and/or modify |
| 8 | * it under the terms of the GNU General Public License version 2 as |
| 9 | * published by the Free Software Foundation. |
| 10 | */ |
| 11 | |
| 12 | #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt |
| 13 | |
| 14 | #include <linux/rtc.h> |
| 15 | |
| 16 | /* IMPORTANT: the RTC only stores whole seconds. It is arbitrary |
| 17 | * whether it stores the most close value or the value with partial |
| 18 | * seconds truncated. However, it is important that we use it to store |
| 19 | * the truncated value. This is because otherwise it is necessary, |
| 20 | * in an rtc sync function, to read both xtime.tv_sec and |
| 21 | * xtime.tv_nsec. On some processors (i.e. ARM), an atomic read |
| 22 | * of >32bits is not possible. So storing the most close value would |
| 23 | * slow down the sync API. So here we have the truncated value and |
| 24 | * the best guess is to add 0.5s. |
| 25 | */ |
| 26 | |
| 27 | static int __init rtc_hctosys(void) |
| 28 | { |
| 29 | int err = -ENODEV; |
| 30 | struct rtc_time tm; |
| 31 | struct timespec64 tv64 = { |
| 32 | .tv_nsec = NSEC_PER_SEC >> 1, |
| 33 | }; |
| 34 | struct rtc_device *rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE); |
| 35 | |
| 36 | if (rtc == NULL) { |
| 37 | pr_info("unable to open rtc device (%s)\n", |
| 38 | CONFIG_RTC_HCTOSYS_DEVICE); |
| 39 | goto err_open; |
| 40 | } |
| 41 | |
| 42 | err = rtc_read_time(rtc, &tm); |
| 43 | if (err) { |
| 44 | dev_err(rtc->dev.parent, |
| 45 | "hctosys: unable to read the hardware clock\n"); |
| 46 | goto err_read; |
| 47 | |
| 48 | } |
| 49 | |
| 50 | tv64.tv_sec = rtc_tm_to_time64(&tm); |
| 51 | |
| 52 | err = do_settimeofday64(&tv64); |
| 53 | |
| 54 | dev_info(rtc->dev.parent, |
| 55 | "setting system clock to " |
| 56 | "%d-%02d-%02d %02d:%02d:%02d UTC (%lld)\n", |
| 57 | tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday, |
| 58 | tm.tm_hour, tm.tm_min, tm.tm_sec, |
| 59 | (long long) tv64.tv_sec); |
| 60 | |
| 61 | err_read: |
| 62 | rtc_class_close(rtc); |
| 63 | |
| 64 | err_open: |
| 65 | rtc_hctosys_ret = err; |
| 66 | |
| 67 | return err; |
| 68 | } |
| 69 | |
| 70 | late_initcall(rtc_hctosys); |