Re: [PATCH v3 2/4] watchdog: da9062: reset board on watchdog timeout

[Andrej Picej <andrej.picej@norik.com>]

Hi Christoph,

On 1. 12. 21 15:11, Christoph Niedermaier wrote:
> From: Andrej Picej
> Sent: Wednesday, December 1, 2021 9:15 AM
>> Implement a method to change watchdog timeout configuration based on DT
>> binding ("dlg,wdt-sd"). There is a possibility to change the bahaviour
>> of watchdog reset. Setting WATCHDOG_SD bit enables SHUTDOWN mode, and
>> clearing it enables POWERDOWN mode on watchdog timeout.
>>
>> If no DT binding is specified the WATCHDOG_SD bit stays in default
>> configuration, not breaking behaviour of devices which might depend on
>> default fuse configuration.
>>
>> Note: This patch requires that the config register CONFIG_I is
>> configured as writable in the da9062 multi function device.
>>
>> Signed-off-by: Andrej Picej <andrej.picej@norik.com>
>> ---
>> Changes in v3:
>>   - no changes
>>
>> Changes in v2:
>>   - don't force the "reset" for all da9062-watchdog users, instead add DT
>>     binding where the behavior can be selected
>> ---
>>   drivers/watchdog/da9062_wdt.c | 25 +++++++++++++++++++++++++
>>   1 file changed, 25 insertions(+)
>>
>> diff --git a/drivers/watchdog/da9062_wdt.c b/drivers/watchdog/da9062_wdt.c
>> index f02cbd530538..e342e9e50cb1 100644
>> --- a/drivers/watchdog/da9062_wdt.c
>> +++ b/drivers/watchdog/da9062_wdt.c
>> @@ -85,8 +85,33 @@ static int da9062_wdt_start(struct watchdog_device *wdd)
>>   {
>>          struct da9062_watchdog *wdt = watchdog_get_drvdata(wdd);
>>          unsigned int selector;
>> +       unsigned int mask;
>> +       u32 val;
>>          int ret;
>>
>> +       /* Configure what happens on watchdog timeout. Can be specified with
>> +        * "dlg,wdt-sd" dt-binding (0 -> POWERDOWN, 1 -> SHUTDOWN).
>> +        * If "dlg,wdt-sd" dt-binding is NOT set use the default.
>> +        */
>> +       ret = device_property_read_u32(wdd->parent, "dlg,wdt-sd", &val);
>> +       if (!ret) {
>> +               if (val)
>> +                       /* Use da9062's SHUTDOWN mode */
>> +                       mask = DA9062AA_WATCHDOG_SD_MASK;
>> +               else
>> +                       /* Use da9062's POWERDOWN mode. */
>> +                       mask = 0x0;
>> +
>> +               ret = regmap_update_bits(wdt->hw->regmap,
>> +                                               DA9062AA_CONFIG_I,
>> +                                               DA9062AA_WATCHDOG_SD_MASK,
>> +                                               mask);
>> +
>> +               if (ret)
>> +                       dev_err(wdt->hw->dev, "failed to set wdt reset mode:
>> %d\n",
>> +                               ret);
>> +       }
>> +
>>          selector = da9062_wdt_timeout_to_sel(wdt->wdtdev.timeout);
>>          ret = da9062_wdt_update_timeout_register(wdt, selector);
>>          if (ret)
>> --
>> 2.25.1
>>
> 
> I have a question how to correctly restart the system after
> watchdog timeout.
> If I understand it correct after watchdog timeout the system
> restarts only if WATCHDOG_SD (Bit 3) in register CONFIG_I is
> set.
> What is the difference if WATCHDOG_SD isn't set, but WAKE_UP
> (Bit 2) in register CONTROL_F is set? From outside on my
> system I observe the same behavior. After watchdog timeout
> my system restarts. So where are the differences?
> It would be nice if you could answer this question, as you
> certainly know this chip very well.

To be honest I don't really know the chip that well, I'm just trying to 
add this feature and hopefully help others if they run into the same 
problem. I think @Adam will be more helpful here.

But from quick look at da9062 datasheet, mainly chapter "8.8 Power 
Modes" I see next main differences:
- setting WATCHDOG_SD enables SHUTDOWN sequence when the watchdog 
timeout is triggered. This puts the chip (da9062) in RESET mode.
Taken from DA9062 datasheet:
> In RESET mode, the internal supplies, and LDO1 (if configured as an always-on supply) are enabled. 
> All other DA9062 supplies are disabled.
> DA9062 is in RESET mode whenever a complete application shutdown is required
> The DA9062’s register configuration will be re-loaded from OTP when leaving the RESET mode

- if you set the WAKE_UP bit than the chip enters POWERDOWN mode on 
watchdog timeout. I understand the POWERDOWN mode as a not that "deep" 
mode as a RESET mode Device will go from RESET mode to POWERDOWN mode in 
the sequence of powering-up.

The above explanation is just my understanding after quick look, @Adam 
please correct me if I'm talking nonsense.

Please have a look at the DA9062 datasheet for more information. Sorry, 
that I can't be more helpful here.

Best regards,
Andrej