linux-kernel - Re: [PATCH v1 1/2] watchdog: dw_wdt: add stop watchdog operation

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Date:   Thu, 14 Sep 2017 12:17:39 +0200
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Oleksij Rempel <o.rempel@...gutronix.de>,
        Wim Van Sebroeck <wim@...ana.be>,
        Guenter Roeck <linux@...ck-us.net>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Cc:     devicetree@...r.kernel.org, linux-watchdog@...r.kernel.org,
        Russell King <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org, kernel@...gutronix.de,
        Steffen Trumtrar <s.trumtrar@...gutronix.de>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v1 1/2] watchdog: dw_wdt: add stop watchdog operation

Hi Oleksij,

On Thu, 2017-09-14 at 10:14 +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
> ---
>  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..50d8a6a5b5ac 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 (IS_ERR(dw_wdt->rst)) {

	if (!dw_wdt->rst) {

Since commit 65a3b6935d92 ("watchdog: dw_wdt: get reset lines from dt"),
the reset control is requested as optional, meaning dw_wdt->rst == NULL
if the reset line is not present. If an error is value is stored into
dw_wdt->rst, the probe function does not succeed.

> +		dev_warn(wdd->parent, "No reset line. Will not
> stop.\n");
> +		return PTR_ERR(dw_wdt->rst);
> +	}

regards
Philipp