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

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Message-ID: <387fadc6-1eab-ada7-86dd-0e47c5e9cb9f@roeck-us.net>
Date:   Tue, 31 Mar 2020 09:08:29 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Adam Thomson <Adam.Thomson.Opensource@...semi.com>,
        Stefan Riedmueller <s.riedmueller@...tec.de>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        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 3/30/20 9:38 AM, Adam Thomson wrote:
> 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.
> 
Agreed.

Guenter

>>
>> 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
>