v4.19.13 snapshot.
diff --git a/drivers/rtc/systohc.c b/drivers/rtc/systohc.c
new file mode 100644
index 0000000..718293d
--- /dev/null
+++ b/drivers/rtc/systohc.c
@@ -0,0 +1,70 @@
+/*
+ * 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.
+ *
+ */
+#include <linux/rtc.h>
+#include <linux/time.h>
+
+/**
+ * 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.
+ *
+ * Returns 0 on successful RTC update, -ENODEV if a RTC update is not
+ * 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, unsigned long *target_nsec)
+{
+ struct rtc_device *rtc;
+ struct rtc_time tm;
+ struct timespec64 to_set;
+ int err = -ENODEV;
+ bool ok;
+
+ rtc = rtc_class_open(CONFIG_RTC_SYSTOHC_DEVICE);
+ 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;
+}