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

[Ariel D'Alessandro <ariel@vanguardiasur.com.ar>]

(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?
> 
>>
>>>>> +
>>>>> +static int lpc_wdt_remove(struct platform_device *pdev)
>>>>> +{
>>>>> +    struct lpc_wdt_dev *lpc_wdt = platform_get_drvdata(pdev);
>>>>> +
>>>>> +    lpc_wdt_stop(&lpc_wdt->wdt_dev);
>>>>
>>>> This will keep the timer enabled. It would be interesting to see what
>>>> happens if you build the driver as module and unload it. I think
>>>> it will crash. Can you try ?
>>>
>>> Yes, you're right. After module gets unloaded, timer keeps enabled with
>>> a callback that was deallocated from memory.
>>>
>>> Since Watchdog cannot be disabled in hardware, it's not going to be
>>> possible to remove the driver without resetting the system. Unless we
>>> could keep a timer set and running outside the module, it won't be
>>> removable.
>>>
>>> What do you think?
>>>
>>
>> My take is that the driver should be loadable as module, which implies
>> that it must be removable. Whoever actually does remove the driver
>> is really asking for trouble and doesn't deserve better.
>>
>> On the other side, there are a few other watchdogs with similar properties.
>> Maybe we can just take guidance from there. Can you have a look ?
>> I can look myself, but it may take a few days.
> 
> Ok. I'm sending patchset v2 with all these modifications.
> 
>>
>> Thanks,
>> Guenter
>>
> --