watchdog: make imx2_wdt report boot status correctly

Ioctl WDIOC_GETBOOTSTATUS is supposed to return some information
on why the system did (re)boot recently, value WDIOF_CARDRESET
being used to indicate watchdog induced reboot.

Up to now, imx2_wdt did not provide a value here, always returning
zero to indicate normal boot.

Do evaluate the IMX Watchdog Reset Status Register and
produce WDIOF_CARDRESET with WDIOC_GETBOOTSTATUS in case
of a watchdog induced reset.

Signed-off-by: Oskar Schirmer <oskar@scara.com>
Acked-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

drivers/watchdog/imx2_wdt.c

@@ -46,6 +46,9 @@
 #define IMX2_WDT_SEQ1		0x5555		/* -> service sequence 1 */
 #define IMX2_WDT_SEQ2		0xAAAA		/* -> service sequence 2 */
 
+#define IMX2_WDT_WRSR		0x04		/* Reset Status Register */
+#define IMX2_WDT_WRSR_TOUT	(1 << 1)	/* -> Reset due to Timeout */
+
 #define IMX2_WDT_MAX_TIME	128
 #define IMX2_WDT_DEFAULT_TIME	60		/* in seconds */
 
@@ -175,16 +178,21 @@ static long imx2_wdt_ioctl(struct file *file, unsigned int cmd,
 	void __user *argp = (void __user *)arg;
 	int __user *p = argp;
 	int new_value;
+	u16 val;
 
 	switch (cmd) {
 	case WDIOC_GETSUPPORT:
 		return copy_to_user(argp, &imx2_wdt_info,
 			sizeof(struct watchdog_info)) ? -EFAULT : 0;
 
 	case WDIOC_GETSTATUS:
-	case WDIOC_GETBOOTSTATUS:
 		return put_user(0, p);
 
+	case WDIOC_GETBOOTSTATUS:
+		val = __raw_readw(imx2_wdt.base + IMX2_WDT_WRSR);
+		new_value = val & IMX2_WDT_WRSR_TOUT ? WDIOF_CARDRESET : 0;
+		return put_user(new_value, p);
+
 	case WDIOC_KEEPALIVE:
 		imx2_wdt_ping();
 		return 0;