drivers/rtc/systohc.c

   1 /*
   2  * This program is free software; you can redistribute it and/or modify it
   3  * under the terms of the GNU General Public License version 2 as published by
   4  * the Free Software Foundation.
   5  *
   6  */
   7 #include <linux/rtc.h>
   8 #include <linux/time.h>
   9
  10 /**
  11  * rtc_set_ntp_time - Save NTP synchronized time to the RTC
  12  * @now: Current time of day
  13  * @target_nsec: pointer for desired now->tv_nsec value
  14  *
  15  * Replacement for the NTP platform function update_persistent_clock64
  16  * that stores time for later retrieval by rtc_hctosys.
  17  *
  18  * Returns 0 on successful RTC update, -ENODEV if a RTC update is not
  19  * possible at all, and various other -errno for specific temporary failure
  20  * cases.
  21  *
  22  * -EPROTO is returned if now.tv_nsec is not close enough to *target_nsec.
  23  *
  24  * If temporary failure is indicated the caller should try again 'soon'
  25  */
  26 int rtc_set_ntp_time(struct timespec64 now, unsigned long *target_nsec)
  27 {
  28         struct rtc_device *rtc;
  29         struct rtc_time tm;
  30         struct timespec64 to_set;
  31         int err = -ENODEV;
  32         bool ok;
  33
  34         rtc = rtc_class_open(CONFIG_RTC_SYSTOHC_DEVICE);
  35         if (!rtc)
  36                 goto out_err;
  37
  38         if (!rtc->ops || (!rtc->ops->set_time && !rtc->ops->set_mmss64 &&
  39                           !rtc->ops->set_mmss))
  40                 goto out_close;
  41
  42         /* Compute the value of tv_nsec we require the caller to supply in
  43          * now.tv_nsec.  This is the value such that (now +
  44          * set_offset_nsec).tv_nsec == 0.
  45          */
  46         set_normalized_timespec64(&to_set, 0, -rtc->set_offset_nsec);
  47         *target_nsec = to_set.tv_nsec;
  48
  49         /* The ntp code must call this with the correct value in tv_nsec, if
  50          * it does not we update target_nsec and return EPROTO to make the ntp
  51          * code try again later.
  52          */
  53         ok = rtc_tv_nsec_ok(rtc->set_offset_nsec, &to_set, &now);
  54         if (!ok) {
  55                 err = -EPROTO;
  56                 goto out_close;
  57         }
  58
  59         rtc_time64_to_tm(to_set.tv_sec, &tm);
  60
  61         /* rtc_hctosys exclusively uses UTC, so we call set_time here, not
  62          * set_mmss.
  63          */
  64         err = rtc_set_time(rtc, &tm);
  65
  66 out_close:
  67         rtc_class_close(rtc);
  68 out_err:
  69         return err;
  70 }