[PATCH 2/2] at91sam9_wdt: Allow watchdog to reset device at early boot

[Rob Herring]

On Mon, Feb 23, 2015 at 10:19 AM, Guenter Roeck <linux at roeck-us.net> wrote:
> On Mon, Feb 23, 2015 at 11:11:38AM +0200, Timo Kokkonen wrote:
> [ ... ]
>
>>
>> After all, we do have already watchdog_init_timeout function that parses the
>> watchdog timeout argument from either device tree or from command line. How
>> about if we expanded that interface? Maybe have a more generic
>> watchdog_init_parmas() or something that parses the generic watchdog
>> arguments, either from command line, device tree or ACPI or something. The
>> device driver could replace call from watchdog_init_timeout() to
>> watchdog_init_params() once it is ready to support other generic parameters,
>> such as early-timeout-sec. Then the watchdog driver could do the right thing
>> about whether watchdog should be left running or stopped and how long time
>> should be given.
>>
> Good idea.
>
>> Alternatively, we could also let the watchdog core know a little more about
>> the actual watchdog hardware, such as whether the HW is stoppable, whether
>> it needs manual pinging by the kernel until user space has taken over. Or

Whether the h/w is stoppable or not is certainly a reasonable DT
property. The maximum h/w timeout would be too (although that may just
be a property of counter size and clock rate).

> Yes, all that will be needed. But, still, the stop-gap is that we'll need to
> get buyin from the DT folks for the necessary properties. I have had the
> outline for the necessary watchdog core implementation in my mind for a long
> time, but I just don't have the time (nor the patience, quite frankly)
> to get DT buyin.

Defining wdog core functionality and behavior has little to do with DT
and you don't need buy in. Presumably you care about non-DT platforms
as well. Moving more of the intelligence to the core would be a good
thing and for the most part should be independent of DT.

Rob

>> maybe we can just extend the timeout values until the user space has first
>> opened it and then shorten the timeout automatically so that it doesn't take
>> that long for the device to reset after a crash. Or some other behaviour
>> that is common to many users. Suggestions are welcome.
>>
>> Anyway, that is something that needs to be done to make watchdog core take
>> more control over more of the generic watchdog behaviour. It just needs to
>> be done so that we don't need to convert all drivers at once.
>>
> Correct. It should not be that difficult do do that if designed properly.
>
> Guenter