[RFC PATCH] watchdog: da9062: Correct the timeout values [Klartext]

[Guenter Roeck]

On 12/13/21 1:11 AM, Christoph Niedermaier wrote:
> Resend with [Klartext] to turn off TLS encryption.
> 
> From: Adam Thomson
> Sent: Monday, December 6, 2021 5:38 PM
>>> Thanks anyway, so now I know it must be
>>> problem with my DA9061 chip.
>>>
>>> @Adam
>>> Where can it come from?
>>> Can you give we a hint what to check?
>>
>> I've spoken internally and have been informed that this is down to the fact that
>> DA9061 runs only from an internal oscillator which may be slower. The indication
>> is that the values for TWDSCALE describe the window where if a kick/ping occurs
>> within that period then the watchdog is guaranteed *not* to timeout. The actual
>> timeout would be at some point after the selected timeout period, assuming no
>> ping/kick occurred.
>>
>> Table 8 in the datasheet specifies a minimum watchdog timeout of 2.5s (tWDMAX)
>> under specific operating conditions, so if the minimum 2s window was chosen
>> (TWDSCALE = 1) then earliest the watchdog would actually timeout, following a
>> ping, is 2.5s, assuming the conditions matched those described.
>>
>> If you have further questions it probably makes sense to contact Dialog/Renesas
>> support as they will be able to provide more detailed info on this.
> 
> So a DA9061 runs only from an internal oscillator, whereas a DA9062
> can run on either an internal or an external oscillator. So this
> means that the DA9061 timeout values are differ from the DA9062
> with an external oscillator not only on my device but on all DA9061
> devices.
> 
> This are the values (in seconds) in comparison:
> DA9062 (from driver): 0  2  4   8  16  32  65 131
> DA9061 (measured):    0  3  6  12  25  51 102 204
> =================================================
> Difference:           0 +1 +2  +4  +9 +19 +37 +73
> 
> In my opinion, the differences in the higher values are very huge.
> If I expect that the watchdog triggers and I have to wait more than
> a minute for that to happen I ask myself is there something wrong.
> 
> @Andrej
> I guess, you are using an external oscillator, aren't you?
> 
> @Adam
> Is there a way to check in the driver which oscillator is in use?
> 
> @Maintainers
> Is in the driver a need to distinguish between an external and an
> internal oscillator to get the timeout values more accurate?
> 

It would be very desirable to get timeout values more accurate.
I would not want to dictate how to implement it, though.
It could be automatically detected if that is possible, there
could be a devicetree clock property providing the clock
frequency, or maybe there is some other solution.

Guenter