linux-kernel - RE: [PATCH 2/3] watchdog: da9063: Use pre configured timeout when watchdog is running

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Message-ID: <AM6PR10MB2263A1A76AFFBCE7BCC4B93880CB0@AM6PR10MB2263.EURPRD10.PROD.OUTLOOK.COM>
Date:   Mon, 30 Mar 2020 16:38:04 +0000
From:   Adam Thomson <Adam.Thomson.Opensource@...semi.com>
To:     Stefan Riedmueller <s.riedmueller@...tec.de>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Support Opensource <Support.Opensource@...semi.com>
CC:     "linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 2/3] watchdog: da9063: Use pre configured timeout when
 watchdog is running

On 26 March 2020 15:02, Stefan Riedmueller wrote:

> If the watchdog is already running during probe use its pre-configured
> timeout instead of a default timeout to make sure the watchdog is pinged
> in time until userspace takes over.

At least for this driver I don't think there's an issue here with regards to
not pinging in time. Calling 'da9063_wdt_update_timeout()', as it currently
does in the probe() when the watchdog is already active, actually disables the
watchdog before then setting a new timeout value, so by that method we're
avoiding a timeout and starting a new timer period.

To my mind the timeout value should come from DT if possible, which I would
assume for the most part would match whatever is defined in the bootloader as
well, unless I'm mistaken. If that's not available though then I would maybe
agree on falling back to a value that was already programmed in the bootloader
rather than the driver default which should be the last resort.

>
> Signed-off-by: Stefan Riedmueller <s.riedmueller@...tec.de>
> ---
>  drivers/watchdog/da9063_wdt.c | 29 ++++++++++++++++++-----------
>  1 file changed, 18 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/watchdog/da9063_wdt.c b/drivers/watchdog/da9063_wdt.c
> index 3d65e92a4e3f..34d0c4f03814 100644
> --- a/drivers/watchdog/da9063_wdt.c
> +++ b/drivers/watchdog/da9063_wdt.c
> @@ -46,15 +46,16 @@ static unsigned int da9063_wdt_timeout_to_sel(unsigned
> int secs)
>  }
>
>  /*
> - * Return 0 if watchdog is disabled, else non zero.
> + * Read the currently active timeout.
> + * Zero means the watchdog is disabled.
>   */
> -static unsigned int da9063_wdt_is_running(struct da9063 *da9063)
> +static unsigned int da9063_wdt_read_timeout(struct da9063 *da9063)
>  {
>  	unsigned int val;
>
>  	regmap_read(da9063->regmap, DA9063_REG_CONTROL_D, &val);
>
> -	return val & DA9063_TWDSCALE_MASK;
> +	return wdt_timeout[val & DA9063_TWDSCALE_MASK];
>  }
>
>  static int da9063_wdt_disable_timer(struct da9063 *da9063)
> @@ -191,6 +192,7 @@ static int da9063_wdt_probe(struct platform_device
> *pdev)
>  	struct device *dev = &pdev->dev;
>  	struct da9063 *da9063;
>  	struct watchdog_device *wdd;
> +	int timeout;
>
>  	if (!dev->parent)
>  		return -EINVAL;
> @@ -214,15 +216,20 @@ static int da9063_wdt_probe(struct platform_device
> *pdev)
>  	watchdog_set_restart_priority(wdd, 128);
>  	watchdog_set_drvdata(wdd, da9063);
>
> -	/* Set default timeout, maybe override it with DT value, scale it */
> -	wdd->timeout = DA9063_WDG_TIMEOUT;
> -	watchdog_init_timeout(wdd, 0, dev);
> -	da9063_wdt_set_timeout(wdd, wdd->timeout);
> -
> -	/* Change the timeout to the default value if the watchdog is running */
> -	if (da9063_wdt_is_running(da9063)) {
> -		da9063_wdt_update_timeout(da9063, wdd->timeout);
> +	/*
> +	 * Use pre-configured timeout if watchdog is already running.
> +	 * Otherwise set default timeout, maybe override it with DT value,
> +	 * scale it
> +	 */
> +	timeout = da9063_wdt_read_timeout(da9063);
> +	if (timeout) {
> +		wdd->timeout = timeout;
>  		set_bit(WDOG_HW_RUNNING, &wdd->status);
> +		dev_info(da9063->dev, "watchdog is running (%u s)", timeout);
> +	} else {
> +		wdd->timeout = DA9063_WDG_TIMEOUT;
> +		watchdog_init_timeout(wdd, 0, dev);
> +		da9063_wdt_set_timeout(wdd, wdd->timeout);
>  	}
>
>  	return devm_watchdog_register_device(dev, wdd);
> --
> 2.23.0