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Subject: Re: [PATCH] RTC: Implement pretimeout watchdog for DS1307
To:     Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Mark Tomlinson <mark.tomlinson@alliedtelesis.co.nz>
Cc:     a.zummo@towertech.it, linux-rtc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-watchdog@vger.kernel.org
References: <20200804051743.19115-1-mark.tomlinson@alliedtelesis.co.nz>
 <20200804152044.GB10725@piout.net>
From:   Guenter Roeck <linux@roeck-us.net>
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Message-ID: <3bb0b209-8213-ce6e-b7ee-3393ca0bbdae@roeck-us.net>
Date:   Tue, 4 Aug 2020 09:14:11 -0700
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On 8/4/20 8:20 AM, Alexandre Belloni wrote:
> Hi,
> 
> The subject prefix is not correct, it should be rtc: ds1307:
> 
> Also, shouldn't that kind of software timeout which doesn't actually
> depend on the hardware better be handled in the watchdog core? Then this
> will benefit all the watchdog and will certainly avoid a lot of code
> duplication.
> 

Good point. I absolutely agree. We'd have to hash out some details,
such as how and when to enable it, but this definitely belongs into
the watchdog core if it is considered useful.

On the other side, the softdog already implements this. Why not just
instantiate the softdog as second watchdog and use it for the purpose
of handling pretimeouts ?

Thanks,
Guenter

> On 04/08/2020 17:17:43+1200, Mark Tomlinson wrote:
>> If the hardware watchdog in the clock chip simply pulls the reset line
>> of the CPU, then there is no chance to write a stack trace to help
>> determine what may have been blocking the CPU.
>>
>> This patch adds a pretimeout to the watchdog, which, if enabled, sets
>> a timer to go off before the hardware watchdog kicks in, and calls
>> the standard pretimeout function, which can (for example) call panic.
>>
>> Signed-off-by: Mark Tomlinson <mark.tomlinson@alliedtelesis.co.nz>
>> ---
>>  drivers/rtc/rtc-ds1307.c | 35 ++++++++++++++++++++++++++++++++++-
>>  1 file changed, 34 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c
>> index 49702942bb08..647f8659d0bd 100644
>> --- a/drivers/rtc/rtc-ds1307.c
>> +++ b/drivers/rtc/rtc-ds1307.c
>> @@ -23,6 +23,7 @@
>>  #include <linux/clk-provider.h>
>>  #include <linux/regmap.h>
>>  #include <linux/watchdog.h>
>> +#include <linux/timer.h>
>>  
>>  /*
>>   * We can't determine type by probing, but if we expect pre-Linux code
>> @@ -174,6 +175,10 @@ struct ds1307 {
>>  #ifdef CONFIG_COMMON_CLK
>>  	struct clk_hw		clks[2];
>>  #endif
>> +#ifdef CONFIG_WATCHDOG_CORE
>> +	struct timer_list	soft_timer;
>> +	struct watchdog_device	*wdt;
>> +#endif
>>  };
>>  
>>  struct chip_desc {
>> @@ -863,12 +868,34 @@ static int m41txx_rtc_set_offset(struct device *dev, long offset)
>>  }
>>  
>>  #ifdef CONFIG_WATCHDOG_CORE
>> +static void ds1388_soft_wdt_expire(struct timer_list *soft_timer)
>> +{
>> +	struct ds1307 *ds1307 = container_of(soft_timer, struct ds1307, soft_timer);
>> +
>> +	watchdog_notify_pretimeout(ds1307->wdt);
>> +}
>> +
>> +static void ds1388_soft_timer_set(struct watchdog_device *wdt_dev)
>> +{
>> +	struct ds1307 *ds1307 = watchdog_get_drvdata(wdt_dev);
>> +	int soft_timeout;
>> +
>> +	if (wdt_dev->pretimeout > 0) {
>> +		soft_timeout = wdt_dev->timeout - wdt_dev->pretimeout;
>> +		mod_timer(&ds1307->soft_timer, jiffies + soft_timeout * HZ);
>> +	} else {
>> +		del_timer(&ds1307->soft_timer);
>> +	}
>> +}
>> +
>>  static int ds1388_wdt_start(struct watchdog_device *wdt_dev)
>>  {
>>  	struct ds1307 *ds1307 = watchdog_get_drvdata(wdt_dev);
>>  	u8 regs[2];
>>  	int ret;
>>  
>> +	ds1388_soft_timer_set(wdt_dev);
>> +
>>  	ret = regmap_update_bits(ds1307->regmap, DS1388_REG_FLAG,
>>  				 DS1388_BIT_WF, 0);
>>  	if (ret)
>> @@ -900,6 +927,7 @@ static int ds1388_wdt_stop(struct watchdog_device *wdt_dev)
>>  {
>>  	struct ds1307 *ds1307 = watchdog_get_drvdata(wdt_dev);
>>  
>> +	del_timer(&ds1307->soft_timer);
>>  	return regmap_update_bits(ds1307->regmap, DS1388_REG_CONTROL,
>>  				  DS1388_BIT_WDE | DS1388_BIT_RST, 0);
>>  }
>> @@ -909,6 +937,7 @@ static int ds1388_wdt_ping(struct watchdog_device *wdt_dev)
>>  	struct ds1307 *ds1307 = watchdog_get_drvdata(wdt_dev);
>>  	u8 regs[2];
>>  
>> +	ds1388_soft_timer_set(wdt_dev);
>>  	return regmap_bulk_read(ds1307->regmap, DS1388_REG_WDOG_HUN_SECS, regs,
>>  				sizeof(regs));
>>  }
>> @@ -923,6 +952,7 @@ static int ds1388_wdt_set_timeout(struct watchdog_device *wdt_dev,
>>  	regs[0] = 0;
>>  	regs[1] = bin2bcd(wdt_dev->timeout);
>>  
>> +	ds1388_soft_timer_set(wdt_dev);
>>  	return regmap_bulk_write(ds1307->regmap, DS1388_REG_WDOG_HUN_SECS, regs,
>>  				 sizeof(regs));
>>  }
>> @@ -1652,7 +1682,8 @@ static void ds1307_clks_register(struct ds1307 *ds1307)
>>  
>>  #ifdef CONFIG_WATCHDOG_CORE
>>  static const struct watchdog_info ds1388_wdt_info = {
>> -	.options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING | WDIOF_MAGICCLOSE,
>> +	.options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING |
>> +		   WDIOF_MAGICCLOSE | WDIOF_PRETIMEOUT,
>>  	.identity = "DS1388 watchdog",
>>  };
>>  
>> @@ -1681,6 +1712,8 @@ static void ds1307_wdt_register(struct ds1307 *ds1307)
>>  	wdt->timeout = 99;
>>  	wdt->max_timeout = 99;
>>  	wdt->min_timeout = 1;
>> +	ds1307->wdt = wdt;
>> +	timer_setup(&ds1307->soft_timer, ds1388_soft_wdt_expire, 0);
>>  
>>  	watchdog_init_timeout(wdt, 0, ds1307->dev);
>>  	watchdog_set_drvdata(wdt, ds1307);
>> -- 
>> 2.28.0
>>
>