watchdog: dw_wdt: Try to get a 30 second watchdog by default

The dw_wdt_set_top() function takes in a value in seconds.  In
dw_wdt_open() we were calling it with a value that's supposed to
represent the maximum value programmed into the "top" register with a
comment saying that we were trying to set the watchdog to its maximum
value.  Instead we ended up setting the watchdog to ~15 seconds.

Let's fix this.  However, setting things to the "max" gives me an 86
second watchdog in the system I'm looking at.  86 seconds feels a
little too long.  We'll explicitly choose 30 seconds as a more
reasonable value.

NOTE: Ideally this driver should be transitioned to be a real watchdog
driver.  Then we could use "watchdog_init_timeout" and let the timeout
be specified in a number of ways (device tree, module parameter, etc).
This patch should be considered a bit of a stopgap solution.

Signed-off-by: Doug Anderson <dianders@chromium.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

drivers/watchdog/dw_wdt.c

@@ -51,6 +51,8 @@
 /* The maximum TOP (timeout period) value that can be set in the watchdog. */
 #define DW_WDT_MAX_TOP		15
 
+#define DW_WDT_DEFAULT_SECONDS	30
+
 static bool nowayout = WATCHDOG_NOWAYOUT;
 module_param(nowayout, bool, 0);
 MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started "
@@ -179,9 +181,9 @@ static int dw_wdt_open(struct inode *inode, struct file *filp)
 	if (!dw_wdt_is_enabled()) {
 		/*
 		 * The watchdog is not currently enabled. Set the timeout to
-		 * the maximum and then start it.
+		 * something reasonable and then start it.
 		 */
-		dw_wdt_set_top(DW_WDT_MAX_TOP);
+		dw_wdt_set_top(DW_WDT_DEFAULT_SECONDS);
 		writel(WDOG_CONTROL_REG_WDT_EN_MASK,
 		       dw_wdt.regs + WDOG_CONTROL_REG_OFFSET);
 	}