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/sun3x/time.c b/arch/m68k/sun3x/time.c
index 7a2c53d9f779..047e2bcee3d7 100644
--- a/arch/m68k/sun3x/time.c
+++ b/arch/m68k/sun3x/time.c
@@ -52,8 +52,8 @@ int sun3x_hwclk(int set, struct rtc_time *t)
 		h->hour = bin2bcd(t->tm_hour);
 		h->wday = bin2bcd(t->tm_wday);
 		h->mday = bin2bcd(t->tm_mday);
-		h->month = bin2bcd(t->tm_mon);
-		h->year = bin2bcd(t->tm_year);
+		h->month = bin2bcd(t->tm_mon + 1);
+		h->year = bin2bcd(t->tm_year % 100);
 		h->csr &= ~C_WRITE;
 	} else {
 		h->csr |= C_READ;
@@ -62,9 +62,11 @@ int sun3x_hwclk(int set, struct rtc_time *t)
 		t->tm_hour = bcd2bin(h->hour);
 		t->tm_wday = bcd2bin(h->wday);
 		t->tm_mday = bcd2bin(h->mday);
-		t->tm_mon = bcd2bin(h->month);
+		t->tm_mon = bcd2bin(h->month) - 1;
 		t->tm_year = bcd2bin(h->year);
 		h->csr &= ~C_READ;
+		if (t->tm_year < 70)
+			t->tm_year += 100;
 	}
 
 	local_irq_restore(flags);