linux-kernel - Re: [PATCH 2/4] watchdog: add support for resetting keepalive timers at start

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Date:   Mon, 2 Mar 2020 15:09:50 +0200
From:   Tero Kristo <t-kristo@...com>
To:     Guenter Roeck <linux@...ck-us.net>
CC:     <wim@...ux-watchdog.org>, <linux-watchdog@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] watchdog: add support for resetting keepalive timers
 at start

On 28/02/2020 19:13, Guenter Roeck wrote:
> On Fri, Feb 28, 2020 at 04:23:29PM +0200, Tero Kristo wrote:
>> Current watchdog core pets the timer always after the initial keepalive
>> time has expired from boot-up. This is incorrect for certain timers that
>> don't like to be petted immediately when they are started, if they have
>> not been running over the boot.
>>
>> To allow drivers to reset their keepalive timers during startup, add
>> a new watchdog flag to the api, WDOG_RESET_KEEPALIVE.
>>
>> Signed-off-by: Tero Kristo <t-kristo@...com>
>> ---
>>   drivers/watchdog/watchdog_dev.c | 2 ++
>>   include/linux/watchdog.h        | 1 +
>>   2 files changed, 3 insertions(+)
>>
>> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
>> index 8b5c742f24e8..131e40c21703 100644
>> --- a/drivers/watchdog/watchdog_dev.c
>> +++ b/drivers/watchdog/watchdog_dev.c
>> @@ -283,6 +283,8 @@ static int watchdog_start(struct watchdog_device *wdd)
>>   		set_bit(WDOG_ACTIVE, &wdd->status);
>>   		wd_data->last_keepalive = started_at;
>>   		watchdog_update_worker(wdd);
>> +		if (test_bit(WDOG_RESET_KEEPALIVE, &wdd->status))
>> +			wd_data->last_hw_keepalive = started_at;
> 
> I don't think the additional flag is needed. The code should just set
> last_hw_keepalive. After all, it already sets last_keepalive, which
> determines when the next internal keepalive will be sent. It makes sense
> to also set last_hw_keepalive to prevent the next keepalive from being
> sent too early.

Ok, I can modify this patch to tweak the last_hw_keepalive 
unconditionally if you think that is safe to do. I did it like this as 
there might be some cases where the existing implementations actually 
expect the ping to happen immediately for some reason (but I guess in 
those cases the corresponding watchdog drivers would need to be modified.)

-Tero
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