linux-kernel - Re: [PATCH v2] gpio_wdt: Add "always

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Date:	Thu, 20 Nov 2014 23:28:17 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Mike Looijmans <mike.looijmans@...ic.nl>, wim@...ana.be
CC:	linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] gpio_wdt: Add "always_running" feature to GPIO watchdog

On 11/20/2014 10:53 PM, Mike Looijmans wrote:
> 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@...ic.nl>
> ---
>
> v2: Rename property "always_running" to "always-running" and add devicetree
> documentation
>
>   .../devicetree/bindings/watchdog/gpio-wdt.txt      |    5 +++++
>   drivers/watchdog/gpio_wdt.c                        |   20 +++++++++++++++++---
>   2 files changed, 22 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/watchdog/gpio-wdt.txt b/Documentation/devicetree/bindings/watchdog/gpio-wdt.txt
> index 37afec1..1987949 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 220a9e0..3266215 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;

Please align columns with the other variables.

>   	unsigned int		hw_algo;
>   	unsigned int		hw_margin;
>   	unsigned long		last_jiffies;
> @@ -56,6 +58,7 @@ static int gpio_wdt_start(struct watchdog_device *wdd)
>   	gpio_direction_output(priv->gpio, priv->state);
>   	priv->last_jiffies = jiffies;
>   	mod_timer(&priv->timer, priv->last_jiffies + priv->hw_margin);
> +	priv->armed = true;
>
>   	return 0;
>   }
> @@ -64,8 +67,11 @@ 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;
>   }
> @@ -91,7 +97,7 @@ 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 +
> +	if (priv->armed && time_after(jiffies, priv->last_jiffies +
>   		       msecs_to_jiffies(wdd->timeout * 1000))) {

Please align continuation lines.

>   		dev_crit(wdd->dev, "Timer expired. System will reboot soon!\n");
>   		return;
> @@ -197,6 +203,9 @@ 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");
> +
Please align continuation line with '('.

>   	watchdog_set_drvdata(&priv->wdd, priv);
>
>   	priv->wdd.info		= &gpio_wdt_ident;
> @@ -218,6 +227,11 @@ static int gpio_wdt_probe(struct platform_device *pdev)
>   	if (ret)
>   		watchdog_unregister_device(&priv->wdd);
>
> +	if (priv->always_running) {
> +		gpio_wdt_start(&priv->wdd);
> +		priv->armed = false;
> +	}
> +

This won't work if there is an error. The driver won't load but the timer
is started, which will likely cause a crash when the timer fires. You'll
have to fix the error handling.

I also dislike that you first set priv->armed in the start function and
then reset it, but I don't have a better idea right now.

Guenter

>   	return ret;
>   }
>
>

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