1 files changed, 70 insertions, 0 deletions

diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
index 5a5ab4fa14f9..d37588f08055 100644
--- a/drivers/rtc/class.c
+++ b/drivers/rtc/class.c
@@ -211,6 +211,73 @@ static int rtc_device_get_id(struct device *dev)
 	return id;
 }
 
+static void rtc_device_get_offset(struct rtc_device *rtc)
+{
+	time64_t range_secs;
+	u32 start_year;
+	int ret;
+
+	/*
+	 * If RTC driver did not implement the range of RTC hardware device,
+	 * then we can not expand the RTC range by adding or subtracting one
+	 * offset.
+	 */
+	if (rtc->range_min == rtc->range_max)
+		return;
+
+	ret = device_property_read_u32(rtc->dev.parent, "start-year",
+				       &start_year);
+	if (!ret) {
+		rtc->start_secs = mktime64(start_year, 1, 1, 0, 0, 0);
+		rtc->set_start_time = true;
+	}
+
+	/*
+	 * If user did not implement the start time for RTC driver, then no
+	 * need to expand the RTC range.
+	 */
+	if (!rtc->set_start_time)
+		return;
+
+	range_secs = rtc->range_max - rtc->range_min + 1;
+
+	/*
+	 * If the start_secs is larger than the maximum seconds (rtc->range_max)
+	 * supported by RTC hardware or the maximum seconds of new expanded
+	 * range (start_secs + rtc->range_max - rtc->range_min) is less than
+	 * rtc->range_min, which means the minimum seconds (rtc->range_min) of
+	 * RTC hardware will be mapped to start_secs by adding one offset, so
+	 * the offset seconds calculation formula should be:
+	 * rtc->offset_secs = rtc->start_secs - rtc->range_min;
+	 *
+	 * If the start_secs is larger than the minimum seconds (rtc->range_min)
+	 * supported by RTC hardware, then there is one region is overlapped
+	 * between the original RTC hardware range and the new expanded range,
+	 * and this overlapped region do not need to be mapped into the new
+	 * expanded range due to it is valid for RTC device. So the minimum
+	 * seconds of RTC hardware (rtc->range_min) should be mapped to
+	 * rtc->range_max + 1, then the offset seconds formula should be:
+	 * rtc->offset_secs = rtc->range_max - rtc->range_min + 1;
+	 *
+	 * If the start_secs is less than the minimum seconds (rtc->range_min),
+	 * which is similar to case 2. So the start_secs should be mapped to
+	 * start_secs + rtc->range_max - rtc->range_min + 1, then the
+	 * offset seconds formula should be:
+	 * rtc->offset_secs = -(rtc->range_max - rtc->range_min + 1);
+	 *
+	 * Otherwise the offset seconds should be 0.
+	 */
+	if (rtc->start_secs > rtc->range_max ||
+	    rtc->start_secs + range_secs - 1 < rtc->range_min)
+		rtc->offset_secs = rtc->start_secs - rtc->range_min;
+	else if (rtc->start_secs > rtc->range_min)
+		rtc->offset_secs = range_secs;
+	else if (rtc->start_secs < rtc->range_min)
+		rtc->offset_secs = -range_secs;
+	else
+		rtc->offset_secs = 0;
+}
+
 /**
  * rtc_device_register - register w/ RTC class
  * @dev: the device to register
@@ -247,6 +314,8 @@ struct rtc_device *rtc_device_register(const char *name, struct device *dev,
 
 	dev_set_name(&rtc->dev, "rtc%d", id);
 
+	rtc_device_get_offset(rtc);
+
 	/* Check to see if there is an ALARM already set in hw */
 	err = __rtc_read_alarm(rtc, &alrm);
 
@@ -436,6 +505,7 @@ int __rtc_register_device(struct module *owner, struct rtc_device *rtc)
 		return -EINVAL;
 
 	rtc->owner = owner;
+	rtc_device_get_offset(rtc);
 
 	/* Check to see if there is an ALARM already set in hw */
 	err = __rtc_read_alarm(rtc, &alrm);