linux-kernel - Re: [PATCH v2 1/2] watchdog: dw_wdt: add stop watchdog operation

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Message-ID: <20170914145208.GC7337@roeck-us.net>
Date:   Thu, 14 Sep 2017 07:52:08 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Oleksij Rempel <o.rempel@...gutronix.de>
Cc:     Wim Van Sebroeck <wim@...ana.be>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Steffen Trumtrar <s.trumtrar@...gutronix.de>,
        linux-watchdog@...r.kernel.org, kernel@...gutronix.de,
        Russell King <linux@...linux.org.uk>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] watchdog: dw_wdt: add stop watchdog operation

On Thu, Sep 14, 2017 at 01:30:12PM +0200, Oleksij Rempel wrote:
> From: Steffen Trumtrar <s.trumtrar@...gutronix.de>
> 
> The only way of stopping the watchdog is by resetting it.
> Add the watchdog op for stopping the device and reset if
> a reset line is provided.
> 
> Signed-off-by: Steffen Trumtrar <s.trumtrar@...gutronix.de>
> Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
> Cc: Wim Van Sebroeck <wim@...ana.be>
> Cc: Guenter Roeck <linux@...ck-us.net>
> Cc: linux-watchdog@...r.kernel.org
> ---
> 
> changes v2:
>  - test if dw_wdt->rst is NULL instead of IS_ERR
> 
>  drivers/watchdog/dw_wdt.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/drivers/watchdog/dw_wdt.c b/drivers/watchdog/dw_wdt.c
> index 36be987ff9ef..a507f36302e1 100644
> --- a/drivers/watchdog/dw_wdt.c
> +++ b/drivers/watchdog/dw_wdt.c
> @@ -135,6 +135,21 @@ static int dw_wdt_start(struct watchdog_device *wdd)
>  	return 0;
>  }
>  
> +static int dw_wdt_stop(struct watchdog_device *wdd)
> +{
> +	struct dw_wdt *dw_wdt = to_dw_wdt(wdd);
> +
> +	if (!dw_wdt->rst) {
> +		dev_warn(wdd->parent, "No reset line. Will not stop.\n");
> +		return -EOPNOTSUPP;

Sorry, not the way to go. It now reports an error to user space when
there was none previously, and it still reboots the system. Plus, this
was a perfectly fine condition previously, and the reset line is optional.
It is not appropriate to generate a warning for a perfectly valid
condition.

You can not change behavior for existing users.

Guenter

> +	}
> +
> +	reset_control_assert(dw_wdt->rst);
> +	reset_control_deassert(dw_wdt->rst);
> +
> +	return 0;
> +}
> +
>  static int dw_wdt_restart(struct watchdog_device *wdd,
>  			  unsigned long action, void *data)
>  {
> @@ -173,6 +188,7 @@ static const struct watchdog_info dw_wdt_ident = {
>  static const struct watchdog_ops dw_wdt_ops = {
>  	.owner		= THIS_MODULE,
>  	.start		= dw_wdt_start,
> +	.stop		= dw_wdt_stop,
>  	.ping		= dw_wdt_ping,
>  	.set_timeout	= dw_wdt_set_timeout,
>  	.get_timeleft	= dw_wdt_get_timeleft,
> -- 
> 2.11.0
>