watchdog: softdog: make pretimeout support a compile option

It occurred to me that the panic pretimeout governor will stall the
softdog, because it is purely software which simply breaks when the
kernel panics. Testing governors with the softdog on the other hand is
really useful, so make this feature a compile time option which nees to
be enabled explicitly. This also removes the overhead if pretimeout
support is not used because it will now be compiled away (saving ~10% on
ARM32).
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/watchdog/Kconfig

@@ -71,6 +71,14 @@ config SOFT_WATCHDOG
 	  To compile this driver as a module, choose M here: the
 	  module will be called softdog.
 
+config SOFT_WATCHDOG_PRETIMEOUT
+	bool "Software watchdog pretimeout governor support"
+	depends on SOFT_WATCHDOG && WATCHDOG_PRETIMEOUT_GOV
+	help
+	  Enable this if you want to use pretimeout governors with the software
+	  watchdog. Be aware that governors might affect the watchdog because it
+	  is purely software, e.g. the panic governor will stall it!
+
 config DA9052_WATCHDOG
 	tristate "Dialog DA9052 Watchdog"
 	depends on PMIC_DA9052 || COMPILE_TEST

drivers/watchdog/softdog.c

@@ -87,11 +87,13 @@ static int softdog_ping(struct watchdog_device *w)
 	if (!mod_timer(&softdog_ticktock, jiffies + (w->timeout * HZ)))
 		__module_get(THIS_MODULE);
 
+	if (IS_ENABLED(CONFIG_SOFT_WATCHDOG_PRETIMEOUT)) {
 		if (w->pretimeout)
 			mod_timer(&softdog_preticktock, jiffies +
 				  (w->timeout - w->pretimeout) * HZ);
 		else
 			del_timer(&softdog_preticktock);
+	}
 
 	return 0;
 }
@@ -101,6 +103,7 @@ static int softdog_stop(struct watchdog_device *w)
 	if (del_timer(&softdog_ticktock))
 		module_put(THIS_MODULE);
 
+	if (IS_ENABLED(CONFIG_SOFT_WATCHDOG_PRETIMEOUT))
 		del_timer(&softdog_preticktock);
 
 	return 0;
@@ -108,8 +111,7 @@ static int softdog_stop(struct watchdog_device *w)
 
 static struct watchdog_info softdog_info = {
 	.identity = "Software Watchdog",
-	.options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING | WDIOF_MAGICCLOSE |
-		   WDIOF_PRETIMEOUT,
+	.options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING | WDIOF_MAGICCLOSE,
 };
 
 static const struct watchdog_ops softdog_ops = {
@@ -134,6 +136,9 @@ static int __init softdog_init(void)
 	watchdog_set_nowayout(&softdog_dev, nowayout);
 	watchdog_stop_on_reboot(&softdog_dev);
 
+	if (IS_ENABLED(CONFIG_SOFT_WATCHDOG_PRETIMEOUT))
+		softdog_info.options |= WDIOF_PRETIMEOUT;
+
 	ret = watchdog_register_device(&softdog_dev);
 	if (ret)
 		return ret;