v4.19.13 snapshot.
diff --git a/drivers/rtc/hctosys.c b/drivers/rtc/hctosys.c
new file mode 100644
index 0000000..b9ec4a1
--- /dev/null
+++ b/drivers/rtc/hctosys.c
@@ -0,0 +1,77 @@
+/*
+ * RTC subsystem, initialize system time on startup
+ *
+ * Copyright (C) 2005 Tower Technologies
+ * Author: Alessandro Zummo <a.zummo@towertech.it>
+ *
+ * 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.
+*/
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/rtc.h>
+
+/* IMPORTANT: the RTC only stores whole seconds. It is arbitrary
+ * whether it stores the most close value or the value with partial
+ * seconds truncated. However, it is important that we use it to store
+ * the truncated value. This is because otherwise it is necessary,
+ * in an rtc sync function, to read both xtime.tv_sec and
+ * xtime.tv_nsec. On some processors (i.e. ARM), an atomic read
+ * of >32bits is not possible. So storing the most close value would
+ * slow down the sync API. So here we have the truncated value and
+ * the best guess is to add 0.5s.
+ */
+
+static int __init rtc_hctosys(void)
+{
+ int err = -ENODEV;
+ struct rtc_time tm;
+ struct timespec64 tv64 = {
+ .tv_nsec = NSEC_PER_SEC >> 1,
+ };
+ struct rtc_device *rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);
+
+ if (rtc == NULL) {
+ pr_info("unable to open rtc device (%s)\n",
+ CONFIG_RTC_HCTOSYS_DEVICE);
+ goto err_open;
+ }
+
+ err = rtc_read_time(rtc, &tm);
+ if (err) {
+ dev_err(rtc->dev.parent,
+ "hctosys: unable to read the hardware clock\n");
+ goto err_read;
+
+ }
+
+ tv64.tv_sec = rtc_tm_to_time64(&tm);
+
+#if BITS_PER_LONG == 32
+ if (tv64.tv_sec > INT_MAX) {
+ err = -ERANGE;
+ goto err_read;
+ }
+#endif
+
+ err = do_settimeofday64(&tv64);
+
+ dev_info(rtc->dev.parent,
+ "setting system clock to "
+ "%d-%02d-%02d %02d:%02d:%02d UTC (%lld)\n",
+ tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
+ tm.tm_hour, tm.tm_min, tm.tm_sec,
+ (long long) tv64.tv_sec);
+
+err_read:
+ rtc_class_close(rtc);
+
+err_open:
+ rtc_hctosys_ret = err;
+
+ return err;
+}
+
+late_initcall(rtc_hctosys);