watchdog: gpio_wdt: Add "always_running" feature to GPIO watchdog

On some chips, like the TPS386000, the trigger cannot be disabled
and the CPU must keep toggling the line at all times. Add a switch
"always_running" to keep toggling the GPIO line regardless of the
state of the soft part of the watchdog. The "armed" member keeps
track of whether a timeout must also cause a reset.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

2 files changed, 34 insertions, 8 deletions

diff --git a/Documentation/devicetree/bindings/watchdog/gpio-wdt.txt b/Documentation/devicetree/bindings/watchdog/gpio-wdt.txt
index 37afec194949..198794963786 100644
--- a/Documentation/devicetree/bindings/watchdog/gpio-wdt.txt
+++ b/Documentation/devicetree/bindings/watchdog/gpio-wdt.txt
@@ -13,6 +13,11 @@ Required Properties:
     by the GPIO flags.
 - hw_margin_ms: Maximum time to reset watchdog circuit (milliseconds).
 
+Optional Properties:
+- always-running: If the watchdog timer cannot be disabled, add this flag to
+  have the driver keep toggling the signal without a client. It will only cease
+  to toggle the signal when the device is open and the timeout elapsed.
+
 Example:
         watchdog: watchdog {
                 /* ADM706 */
diff --git a/drivers/watchdog/gpio_wdt.c b/drivers/watchdog/gpio_wdt.c
index bbdb19b45332..cbc313d37c59 100644
--- a/drivers/watchdog/gpio_wdt.c
+++ b/drivers/watchdog/gpio_wdt.c
@@ -31,6 +31,8 @@ struct gpio_wdt_priv {
         int                     gpio;
         bool                    active_low;
         bool                    state;
+        bool                    always_running;
+        bool                    armed;
         unsigned int            hw_algo;
         unsigned int            hw_margin;
         unsigned long           last_jiffies;
@@ -48,14 +50,20 @@ static void gpio_wdt_disable(struct gpio_wdt_priv *priv)
                 gpio_direction_input(priv->gpio);
 }
 
-static int gpio_wdt_start(struct watchdog_device *wdd)
+static void gpio_wdt_start_impl(struct gpio_wdt_priv *priv)
 {
-        struct gpio_wdt_priv *priv = watchdog_get_drvdata(wdd);
-
         priv->state = priv->active_low;
         gpio_direction_output(priv->gpio, priv->state);
         priv->last_jiffies = jiffies;
         mod_timer(&priv->timer, priv->last_jiffies + priv->hw_margin);
+}
+
+static int gpio_wdt_start(struct watchdog_device *wdd)
+{
+        struct gpio_wdt_priv *priv = watchdog_get_drvdata(wdd);
+
+        gpio_wdt_start_impl(priv);
+        priv->armed = true;
 
         return 0;
 }
@@ -64,8 +72,11 @@ static int gpio_wdt_stop(struct watchdog_device *wdd)
 {
         struct gpio_wdt_priv *priv = watchdog_get_drvdata(wdd);
 
-        mod_timer(&priv->timer, 0);
-        gpio_wdt_disable(priv);
+        priv->armed = false;
+        if (!priv->always_running) {
+                mod_timer(&priv->timer, 0);
+                gpio_wdt_disable(priv);
+        }
 
         return 0;
 }
@@ -91,8 +102,8 @@ static void gpio_wdt_hwping(unsigned long data)
         struct watchdog_device *wdd = (struct watchdog_device *)data;
         struct gpio_wdt_priv *priv = watchdog_get_drvdata(wdd);
 
-        if (time_after(jiffies, priv->last_jiffies +
-                       msecs_to_jiffies(wdd->timeout * 1000))) {
+        if (priv->armed && time_after(jiffies, priv->last_jiffies +
+                                      msecs_to_jiffies(wdd->timeout * 1000))) {
                 dev_crit(wdd->dev, "Timer expired. System will reboot soon!\n");
                 return;
         }
@@ -197,6 +208,9 @@ static int gpio_wdt_probe(struct platform_device *pdev)
         /* Use safe value (1/2 of real timeout) */
         priv->hw_margin = msecs_to_jiffies(hw_margin / 2);
 
+        priv->always_running = of_property_read_bool(pdev->dev.of_node,
+                                                     "always-running");
+
         watchdog_set_drvdata(&priv->wdd, priv);
 
         priv->wdd.info          = &gpio_wdt_ident;
@@ -216,8 +230,15 @@ static int gpio_wdt_probe(struct platform_device *pdev)
         priv->notifier.notifier_call = gpio_wdt_notify_sys;
         ret = register_reboot_notifier(&priv->notifier);
         if (ret)
-                watchdog_unregister_device(&priv->wdd);
+                goto error_unregister;
 
+        if (priv->always_running)
+                gpio_wdt_start_impl(priv);
+
+        return 0;
+
+error_unregister:
+        watchdog_unregister_device(&priv->wdd);
         return ret;
 }