1 files changed, 69 insertions, 0 deletions
diff --git a/drivers/rtc/hctosys.c b/drivers/rtc/hctosys.c
new file mode 100644
index 00000000000000..d02fe9a0001fcf
--- /dev/null
+++ b/drivers/rtc/hctosys.c
@@ -0,0 +1,69 @@
+/*
+ * 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.
+*/
+
+#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;
+	struct rtc_time tm;
+	struct class_device *class_dev = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);
+
+	if (class_dev == NULL) {
+		printk("%s: unable to open rtc device (%s)\n",
+			__FILE__, CONFIG_RTC_HCTOSYS_DEVICE);
+		return -ENODEV;
+	}
+
+	err = rtc_read_time(class_dev, &tm);
+	if (err == 0) {
+		err = rtc_valid_tm(&tm);
+		if (err == 0) {
+			struct timespec tv;
+
+			tv.tv_nsec = NSEC_PER_SEC >> 1;
+
+			rtc_tm_to_time(&tm, &tv.tv_sec);
+
+			do_settimeofday(&tv);
+
+			dev_info(class_dev->dev,
+				"setting the system clock to "
+				"%d-%02d-%02d %02d:%02d:%02d (%u)\n",
+				tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
+				tm.tm_hour, tm.tm_min, tm.tm_sec,
+				(unsigned int) tv.tv_sec);
+		}
+		else
+			dev_err(class_dev->dev,
+				"hctosys: invalid date/time\n");
+	}
+	else
+		dev_err(class_dev->dev,
+			"hctosys: unable to read the hardware clock\n");
+
+	rtc_class_close(class_dev);
+
+	return 0;
+}
+
+late_initcall(rtc_hctosys);