1 files changed, 70 insertions, 0 deletions
diff --git a/drivers/rtc/hctosys.c b/drivers/rtc/hctosys.c
new file mode 100644
index 000000000..e1cfa0681
--- /dev/null
+++ b/drivers/rtc/hctosys.c
@@ -0,0 +1,70 @@
+/*
+ * 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);
+
+	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);