Re: [RFC] watchdog: renesas_wdt: don't keep timer value during suspend/resume

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

On 12/7/18 1:45 PM, Wolfram Sang wrote:
> Hi Guenter, all,
> 
>>> After discussing this mail thread [1] again, we concluded that giving
>>> userspace enough time to prepare is our favourite option. So, do not
>>> keep the time value when suspended but reset it when resuming.
>>>
>>> [1] https://patchwork.kernel.org/patch/10252209/
>>>
>>> Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
>>
>> Above exchange says it all, no need to repeat.
>>
>> Reviewed-by: Guenter Roeck <linux@roeck-us.net>
> 
> Thanks.
> 
> I can relate to the policy argument, though. Regardless of this patch, I
> wonder if we can make it configurable from userspace. A draft:
> 
> #define	WDIOF_RESUME_OPTS	0x0800
> 
> #define	WDIOS_RESUME_KEEP	0x0008
> #define	WDIOS_RESUME_RESET	0x0010
> 
> and then in watchdog_ioctl() under WDIOC_SETOPTIONS:
> 
> 	if (!(wdd->info->options & WDIOF_RESUME_OPTS))
> 		err = -EOPNOTSUPP;
> 		goto break;
> 
> 	if (val & WDIOS_RESUME_KEEP)
> 		wdd->status |= WDOG_KEEP_TIMER_WHEN_RESUME;
> 
> 	if (val & WDIOS_RESUME_RESET)
> 		wdd->status ~= ~WDOG_KEEP_TIMER_WHEN_RESUME;
> 
> So, drivers with WDIOF_RESUME_OPTS could act on the
> WDOG_KEEP_TIMER_WHEN_RESUME flag.
> 
> Opinions?
> 

Not entirely sure I understand the use case.

Having said that, if we were to add this option, I think only a single
flag would be needed - WDIOF_RESUME_KEEP. All we need to do is declare
that a ping on resume shall be the default. Anything else would result
in undefined per-driver default behavior.

Guenter