drivers/rtc/systohc.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/rtc.h>
   3 #include <linux/time.h>
   4
   5 /**
   6  * rtc_set_ntp_time - Save NTP synchronized time to the RTC
   7  * @now: Current time of day
   8  * @target_nsec: pointer for desired now->tv_nsec value
   9  *
  10  * Replacement for the NTP platform function update_persistent_clock64
  11  * that stores time for later retrieval by rtc_hctosys.
  12  *
  13  * Returns 0 on successful RTC update, -ENODEV if a RTC update is not
  14  * possible at all, and various other -errno for specific temporary failure
  15  * cases.
  16  *
  17  * -EPROTO is returned if now.tv_nsec is not close enough to *target_nsec.
  18  *
  19  * If temporary failure is indicated the caller should try again 'soon'
  20  */
  21 int rtc_set_ntp_time(struct timespec64 now, unsigned long *target_nsec)
  22 {
  23         struct rtc_device *rtc;
  24         struct rtc_time tm;
  25         struct timespec64 to_set;
  26         int err = -ENODEV;
  27         bool ok;
  28
  29         rtc = rtc_class_open(CONFIG_RTC_SYSTOHC_DEVICE);
  30         if (!rtc)
  31                 goto out_err;
  32
  33         if (!rtc->ops || !rtc->ops->set_time)
  34                 goto out_close;
  35
  36         /* Compute the value of tv_nsec we require the caller to supply in
  37          * now.tv_nsec.  This is the value such that (now +
  38          * set_offset_nsec).tv_nsec == 0.
  39          */
  40         set_normalized_timespec64(&to_set, 0, -rtc->set_offset_nsec);
  41         *target_nsec = to_set.tv_nsec;
  42
  43         /* The ntp code must call this with the correct value in tv_nsec, if
  44          * it does not we update target_nsec and return EPROTO to make the ntp
  45          * code try again later.
  46          */
  47         ok = rtc_tv_nsec_ok(rtc->set_offset_nsec, &to_set, &now);
  48         if (!ok) {
  49                 err = -EPROTO;
  50                 goto out_close;
  51         }
  52
  53         rtc_time64_to_tm(to_set.tv_sec, &tm);
  54
  55         err = rtc_set_time(rtc, &tm);
  56
  57 out_close:
  58         rtc_class_close(rtc);
  59 out_err:
  60         return err;
  61 }