m68k: Fix off-by-one calendar month

This fixes a bug in read_persistent_clock() which causes the system
clock to lag the Real Time Clock by one month. The problem was noticed
on a Mac, but theoretically it must also affect Atari, BVME6000 and Q40.

The tm_mon value in the struct rtc_time passed to mach_hwclk() is
zero-based, and atari_mste_hwclk(), atari_tt_hwclk(), bvme6000_hwclk(),
mac_hwclk() and q40_hwclk() all make this adjustment. Unfortunately,
dn_dummy_hwclk(), mvme147_hwclk(), mvme16x_hwclk(), sun3_hwclk() and
sun3x_hwclk() fail to decrement tm_mon.  Also m68328_hwclk() assumes
a one-based tm_mon.

Bring these platforms into line and fix read_persistent_clock() so it
works correctly on all m68k platforms.

The datasheets for the RTC devices found on the affected platforms
all confirm that the year is stored as a value in the range 0-99 and
the month is stored as a value in the range 1-12. Please refer to the
datasheets for MC146818 (Apollo), DS1643 (MVME), ICM7170 (Sun 3)
and M48T02 (Sun 3x).

Reported-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

1 files changed, 5 insertions, 3 deletions

diff --git a/arch/m68k/apollo/config.c b/arch/m68k/apollo/config.c
index 0d27706f14d4..b2a6bc63f8cd 100644
--- a/arch/m68k/apollo/config.c
+++ b/arch/m68k/apollo/config.c
@@ -221,8 +221,10 @@ int dn_dummy_hwclk(int op, struct rtc_time *t) {
     t->tm_hour=rtc->hours;
     t->tm_mday=rtc->day_of_month;
     t->tm_wday=rtc->day_of_week;
-    t->tm_mon=rtc->month;
+    t->tm_mon = rtc->month - 1;
     t->tm_year=rtc->year;
+    if (t->tm_year < 70)
+	t->tm_year += 100;
   } else {
     rtc->second=t->tm_sec;
     rtc->minute=t->tm_min;
@@ -230,8 +232,8 @@ int dn_dummy_hwclk(int op, struct rtc_time *t) {
     rtc->day_of_month=t->tm_mday;
     if(t->tm_wday!=-1)
       rtc->day_of_week=t->tm_wday;
-    rtc->month=t->tm_mon;
-    rtc->year=t->tm_year;
+    rtc->month = t->tm_mon + 1;
+    rtc->year = t->tm_year % 100;
   }
 
   return 0;