linux-kernel - Re: [PATCH v10 3/3] watchdog: make the device time out at open_deadline when open

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Date:   Fri, 7 Jun 2019 11:38:27 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>
Cc:     "linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Jonathan Corbet <corbet@....net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        Esben Haabendal <esben@...bendal.dk>,
        Jerry Hoemann <jerry.hoemann@....com>,
        Rasmus Villemoes <Rasmus.Villemoes@...vas.se>
Subject: Re: [PATCH v10 3/3] watchdog: make the device time out at
 open_deadline when open_timeout is used

On Wed, Jun 05, 2019 at 02:06:44PM +0000, Rasmus Villemoes wrote:
> When the watchdog device is not open by userspace, the kernel takes
> care of pinging it. When the open_timeout feature is in use, we should
> ensure that the hardware fires close to open_timeout seconds after the
> kernel has assumed responsibility for the device.
> 
> To do this, simply reuse the logic that is already in place for
> ensuring the same thing when userspace is responsible for regularly
> pinging the device:
> 
> - When watchdog_active(wdd), this patch doesn't change anything.
> 
> - When !watchdoc_active(wdd), the "virtual timeout" should be taken to

s/watchdoc_active/watchdog_active/

otherwise

Reviewed-by: Guenter Roeck <linux@...ck-us.net>

> be ->open_deadline". When the open_timeout feature is not used or the
> device has been opened at least once, ->open_deadline is KTIME_MAX,
> and the arithmetic ends up returning keepalive_interval as we used to.
> 
> This has been tested on a Wandboard with various combinations of
> open_timeout and timeout-sec properties for the on-board watchdog by
> booting with 'init=/bin/sh', timestamping the lines on the serial
> console, and comparing the timestamp of the 'imx2-wdt 20bc000.wdog:
> timeout nnn sec' line with the timestamp of the 'U-Boot SPL ...'
> line (which appears just after reset).
> 
> Suggested-by: Guenter Roeck <linux@...ck-us.net>
> Signed-off-by: Rasmus Villemoes <rasmus.villemoes@...vas.dk>
> ---
>  drivers/watchdog/watchdog_dev.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
> index 334b810db2cf..edfb884044e0 100644
> --- a/drivers/watchdog/watchdog_dev.c
> +++ b/drivers/watchdog/watchdog_dev.c
> @@ -133,14 +133,15 @@ static ktime_t watchdog_next_keepalive(struct watchdog_device *wdd)
>  	ktime_t virt_timeout;
>  	unsigned int hw_heartbeat_ms;
>  
> -	virt_timeout = ktime_add(wd_data->last_keepalive,
> -				 ms_to_ktime(timeout_ms));
> +	if (watchdog_active(wdd))
> +		virt_timeout = ktime_add(wd_data->last_keepalive,
> +					 ms_to_ktime(timeout_ms));
> +	else
> +		virt_timeout = wd_data->open_deadline;
> +
>  	hw_heartbeat_ms = min_not_zero(timeout_ms, wdd->max_hw_heartbeat_ms);
>  	keepalive_interval = ms_to_ktime(hw_heartbeat_ms / 2);
>  
> -	if (!watchdog_active(wdd))
> -		return keepalive_interval;
> -
>  	/*
>  	 * To ensure that the watchdog times out wdd->timeout seconds
>  	 * after the most recent ping from userspace, the last