1 files changed, 38 insertions, 15 deletions

diff --git a/drivers/rtc/systohc.c b/drivers/rtc/systohc.c
index b4a68ffcd06b..0c177647ea6c 100644
--- a/drivers/rtc/systohc.c
+++ b/drivers/rtc/systohc.c
@@ -10,6 +10,7 @@
 /**
  * rtc_set_ntp_time - Save NTP synchronized time to the RTC
  * @now: Current time of day
+ * @target_nsec: pointer for desired now->tv_nsec value
  *
  * Replacement for the NTP platform function update_persistent_clock64
  * that stores time for later retrieval by rtc_hctosys.
@@ -18,30 +19,52 @@
  * possible at all, and various other -errno for specific temporary failure
  * cases.
  *
+ * -EPROTO is returned if now.tv_nsec is not close enough to *target_nsec.
+ (
  * If temporary failure is indicated the caller should try again 'soon'
  */
-int rtc_set_ntp_time(struct timespec64 now)
+int rtc_set_ntp_time(struct timespec64 now, unsigned long *target_nsec)
 {
 	struct rtc_device *rtc;
 	struct rtc_time tm;
+	struct timespec64 to_set;
 	int err = -ENODEV;
-
-	if (now.tv_nsec < (NSEC_PER_SEC >> 1))
-		rtc_time64_to_tm(now.tv_sec, &tm);
-	else
-		rtc_time64_to_tm(now.tv_sec + 1, &tm);
+	bool ok;
 
 	rtc = rtc_class_open(CONFIG_RTC_SYSTOHC_DEVICE);
-	if (rtc) {
-		/* rtc_hctosys exclusively uses UTC, so we call set_time here,
-		 * not set_mmss. */
-		if (rtc->ops &&
-		    (rtc->ops->set_time ||
-		     rtc->ops->set_mmss64 ||
-		     rtc->ops->set_mmss))
-			err = rtc_set_time(rtc, &tm);
-		rtc_class_close(rtc);
+	if (!rtc)
+		goto out_err;
+
+	if (!rtc->ops || (!rtc->ops->set_time && !rtc->ops->set_mmss64 &&
+			  !rtc->ops->set_mmss))
+		goto out_close;
+
+	/* Compute the value of tv_nsec we require the caller to supply in
+	 * now.tv_nsec.  This is the value such that (now +
+	 * set_offset_nsec).tv_nsec == 0.
+	 */
+	set_normalized_timespec64(&to_set, 0, -rtc->set_offset_nsec);
+	*target_nsec = to_set.tv_nsec;
+
+	/* The ntp code must call this with the correct value in tv_nsec, if
+	 * it does not we update target_nsec and return EPROTO to make the ntp
+	 * code try again later.
+	 */
+	ok = rtc_tv_nsec_ok(rtc->set_offset_nsec, &to_set, &now);
+	if (!ok) {
+		err = -EPROTO;
+		goto out_close;
 	}
 
+	rtc_time64_to_tm(to_set.tv_sec, &tm);
+
+	/* rtc_hctosys exclusively uses UTC, so we call set_time here, not
+	 * set_mmss.
+	 */
+	err = rtc_set_time(rtc, &tm);
+
+out_close:
+	rtc_class_close(rtc);
+out_err:
 	return err;
 }