[PATCH] vrtc: change its year offset from 1960 to 1972

[Alan Cox <alan@lxorguk.ukuu.org.uk>]

From: Feng Tang <feng.tang@intel.com>

Real world year equals the value in vrtc YEAR register plus an offset.
We used 1960 for original developepment  as the offset to make leap year
consistent, but for a device's first use, its YEAR register is 0 and the
system year will be parsed as 1960 which is not a valid UNIX time and will
cause many applications to fail mysteriously. Devices use 1972 instead to
fix this issue.

Updated patch which adds a sanity check suggested by Mathias

Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
---

 arch/x86/platform/mrst/vrtc.c |    4 ++--
 drivers/rtc/rtc-mrst.c        |   19 +++++++++++--------
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/arch/x86/platform/mrst/vrtc.c b/arch/x86/platform/mrst/vrtc.c
index 901e622..8efb035 100644
--- a/arch/x86/platform/mrst/vrtc.c
+++ b/arch/x86/platform/mrst/vrtc.c
@@ -71,8 +71,8 @@ unsigned long vrtc_get_time(void)
 	mon = vrtc_cmos_read(RTC_MONTH);
 	year = vrtc_cmos_read(RTC_YEAR);
 
-	/* vRTC YEAR reg contains the offset to 1960 */
-	year += 1960;
+	/* vRTC YEAR reg contains the offset to 1972 */
+	year += 1972;
 
 	printk(KERN_INFO "vRTC: sec: %d min: %d hour: %d day: %d "
 		"mon: %d year: %d\n", sec, min, hour, mday, mon, year);
diff --git a/drivers/rtc/rtc-mrst.c b/drivers/rtc/rtc-mrst.c
index d335448..bb21f44 100644
--- a/drivers/rtc/rtc-mrst.c
+++ b/drivers/rtc/rtc-mrst.c
@@ -76,12 +76,15 @@ static inline unsigned char vrtc_is_updating(void)
 /*
  * rtc_time's year contains the increment over 1900, but vRTC's YEAR
  * register can't be programmed to value larger than 0x64, so vRTC
- * driver chose to use 1960 (1970 is UNIX time start point) as the base,
+ * driver chose to use 1972 (1970 is UNIX time start point) as the base,
  * and does the translation at read/write time.
  *
- * Why not just use 1970 as the offset? it's because using 1960 will
+ * Why not just use 1970 as the offset? it's because using 1972 will
  * make it consistent in leap year setting for both vrtc and low-level
- * physical rtc devices.
+ * physical rtc devices. Then why not use 1960 as the offset? If we use
+ * 1960, for a device's first use, its YEAR register is 0 and the system
+ * year will be parsed as 1960 which is not a valid UNIX time and will
+ * cause many applications to fail mysteriously.
  */
 static int mrst_read_time(struct device *dev, struct rtc_time *time)
 {
@@ -99,10 +102,10 @@ static int mrst_read_time(struct device *dev, struct rtc_time *time)
 	time->tm_year = vrtc_cmos_read(RTC_YEAR);
 	spin_unlock_irqrestore(&rtc_lock, flags);
 
-	/* Adjust for the 1960/1900 */
-	time->tm_year += 60;
+	/* Adjust for the 1972/1900 */
+	time->tm_year += 72;
 	time->tm_mon--;
-	return RTC_24H;
+	return rtc_valid_tm(time);
 }
 
 static int mrst_set_time(struct device *dev, struct rtc_time *time)
@@ -119,9 +122,9 @@ static int mrst_set_time(struct device *dev, struct rtc_time *time)
 	min = time->tm_min;
 	sec = time->tm_sec;
 
-	if (yrs < 70 || yrs > 138)
+	if (yrs < 72 || yrs > 138)
 		return -EINVAL;
-	yrs -= 60;
+	yrs -= 72;
 
 	spin_lock_irqsave(&rtc_lock, flags);