Re: [PATCH 1/2] watchdog: NXP LPC18XX Windowed Watchdog Timer Driver

[Guenter Roeck <linux@roeck-us.net>]

On 07/01/2015 05:02 AM, Ariel D'Alessandro wrote:
> (Sorry, I sent the last mail with an incorrect mail account)
>
> El 01/07/15 a las 08:30, adalessandro escibió:
>>
>> El 29/06/15 a las 01:47, Guenter Roeck escibió:
>>> On 06/28/2015 11:13 AM, Ariel D'Alessandro wrote:
>>>>>> +/* Timeout values in seconds */
>>>>>> +#define LPC_WDT_DEF_TIMEOUT        1
>>>>>> +
>>>>>
>>>>> One second ? This is highly unusual. 30 or 60 seconds is more common,
>>>>> and one second would be very challenging for user space.
>>>>>
>>>>> Any special reason for using such a tight default ?
>>>>
>>>> Considering that LPC18xx Watchdog has a fixed divide-by-4 clock
>>>> pre-scaler and a 24-bit counter and that Watchdog clock runs at a fixed
>>>> frequency of 12MHz, timeout range goes from 1 to 5 seconds.
>>>>
>>>> I think you're right, 1 sec is very challenging, so it's 5 secs then.
>>>>
>>> Ultimately you might want to consider a soft timer as backup to the system
>>> timeout. But that can be done later if/when needed.
>>
>> I understand your point, but just to be sure, what do mean by soft timer?
>>

A kernel function which pings the watchdog periodically even if the
watchdog is open.

Example: Timeout is set to 30 seconds. Since the HW watchdog times out
earlier than that, it needs to be pinged regularly (eg every 2.5 seconds).
The kernel does that with a timer unless user space does not ping the
watchdog within the configured interval of 30 seconds.

Guenter