[PATCH] i2c: fix broken ds1337 initialization

On a custom board with ds1337 RTC I found that upgrade from 2.6.15 to
2.6.18 broke RTC support.

The main problem are changes to ds1337_init_client().
When a ds1337 recognizes a problem (e.g. power or clock failure) bit 7
in status register is set. This has to be reset by writing 0 to status
register. But since there are only 16 byte written to the chip and the
first byte is interpreted as an address, the status register (which is
the 16th) is never written.
The other problem is, that initializing all registers to zero is not
valid for day, date and month register. Funny enough this is checked by
ds1337_detect(), which depends on this values not being zero. So then
treated by ds1337_init_client() the ds1337 is not detected anymore,
whereas the failure bit in the status register is still set.

Broken by commit f9e89579 (2.6.16-rc1,
2006-01-06). This fix is in Linus' tree since 2.6.20-rc1 (commit
763d9c04).
Signed-off-by: Dirk Stieler <stieler@gdsys.de>
Signed-off-by: Dirk Eibach <eibach@gdsys.de>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>

drivers/i2c/chips/ds1337.c

@@ -347,13 +347,19 @@ static void ds1337_init_client(struct i2c_client *client)
 
 	if ((status & 0x80) || (control & 0x80)) {
 		/* RTC not running */
-		u8 buf[16];
+		u8 buf[1+16];	/* First byte is interpreted as address */
 		struct i2c_msg msg[1];
 
 		dev_dbg(&client->dev, "%s: RTC not running!\n", __FUNCTION__);
 
 		/* Initialize all, including STATUS and CONTROL to zero */
 		memset(buf, 0, sizeof(buf));
+
+		/* Write valid values in the date/time registers */
+		buf[1+DS1337_REG_DAY] = 1;
+		buf[1+DS1337_REG_DATE] = 1;
+		buf[1+DS1337_REG_MONTH] = 1;
+
 		msg[0].addr = client->addr;
 		msg[0].flags = 0;
 		msg[0].len = sizeof(buf);