[PATCH] x86, mrst: add explalation for using 1960 as the year offset for vrtc device

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

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

Explain the reason for the apparently odd choice of year offset so we don't
get more questions about it.

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

 drivers/rtc/rtc-mrst.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)


diff --git a/drivers/rtc/rtc-mrst.c b/drivers/rtc/rtc-mrst.c
index 67b6be2..bcd0cf6 100644
--- a/drivers/rtc/rtc-mrst.c
+++ b/drivers/rtc/rtc-mrst.c
@@ -66,7 +66,11 @@ static inline int is_intr(u8 rtc_intr)
  * 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,
- * and does the translation at read/write time
+ * and does the translation at read/write time.
+ *
+ * Why not just use 1970 as the offset? it's because using 1960 will
+ * make it consistent in leap year setting for both vrtc and low-level
+ * physical rtc devices.
  */
 static int mrst_read_time(struct device *dev, struct rtc_time *time)
 {