Re: [PATCH v1 1/1] driver: watchdog: Remove mtk_wdt_stop() in probe() to prevent the system freeze and it doesn't reboot by watchdog problem

[Freddy.Hsin <freddy.hsin@mediatek.com>]

On Fri, 2020-12-25 at 22:27 +0800, Guenter Roeck wrote:
> On 12/24/20 11:30 PM, Freddy Hsin wrote:
> > From: "freddy.hsin" <freddy.hsin@mediatek.com>
> > 
> > Before user space daemon start to access the watchdog device,
> > there is a time interval that watchdog is disabled in the
> > original flow. If the system freezing at this interval, it
> > cannot be rebooted by watchdog hardware automatically.
> > 
> > In order to solve this problem, the watchdog hardware should be
> > kept working, and start hrtimer in framework to ping it by
> > setting max_hw_heartbeat_ms and HW_RUNNING used in
> > watchdog_need_worker to determine whether the worker should be
> > started or not
> > 
> > Change-Id: I6a041b0922888a90011d7538ee804d80bc8d15ea
> > Signed-off-by: freddy.hsin <freddy.hsin@mediatek.com>
> > ---
> >  drivers/watchdog/mtk_wdt.c |   22 ++++++++++++++++++----
> >  1 file changed, 18 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/watchdog/mtk_wdt.c b/drivers/watchdog/mtk_wdt.c
> > index d6a6393..62f08cd 100644
> > --- a/drivers/watchdog/mtk_wdt.c
> > +++ b/drivers/watchdog/mtk_wdt.c
> > @@ -195,6 +195,19 @@ static int mtk_wdt_set_timeout(struct watchdog_device *wdt_dev,
> >  	return 0;
> >  }
> >  
> > +static void mtk_wdt_init(struct watchdog_device *wdt_dev)
> > +{
> > +	struct mtk_wdt_dev *mtk_wdt = watchdog_get_drvdata(wdt_dev);
> > +	void __iomem *wdt_base;
> > +
> > +	wdt_base = mtk_wdt->wdt_base;
> > +
> > +	if (readl(wdt_base + WDT_MODE) & WDT_MODE_EN) {
> > +		set_bit(WDOG_HW_RUNNING, &wdt_dev->status);
> > +		mtk_wdt_set_timeout(wdt_dev, wdt_dev->timeout);
> > +	}
> > +}
> > +
> >  static int mtk_wdt_stop(struct watchdog_device *wdt_dev)
> >  {
> >  	struct mtk_wdt_dev *mtk_wdt = watchdog_get_drvdata(wdt_dev);
> > @@ -266,16 +279,17 @@ static int mtk_wdt_probe(struct platform_device *pdev)
> >  	mtk_wdt->wdt_dev.timeout = WDT_MAX_TIMEOUT;
> >  	mtk_wdt->wdt_dev.max_timeout = WDT_MAX_TIMEOUT;
> 
> No longer needed if max_hw_heartbeat_ms is set.

Got it. it will be removed in V2 patch

> 
> >  	mtk_wdt->wdt_dev.min_timeout = WDT_MIN_TIMEOUT;
> > +	mtk_wdt->wdt_dev.max_hw_heartbeat_ms = (WDT_MAX_TIMEOUT - 1) * 1000;
> 
> This needs explanation. Why WDT_MAX_TIMEOUT - 1 ?

In watchdog_need_worker(), there is a condition for starting worker (hm
&& watchdog_active(wdd) && t > hm), so I think in the case
that watchdog_active is true, the t (timeout) should be greater than
hm (max_hw_heartbeat_ms) or the worker will not work. Shouldn't I
consider for this case?

> 
> >  	mtk_wdt->wdt_dev.parent = dev;
> >  
> > +	watchdog_set_drvdata(&mtk_wdt->wdt_dev, mtk_wdt);
> > +
> > +	mtk_wdt_init(&mtk_wdt->wdt_dev);
> > +
> 
> Setting the chip (with the maximum timeout) ...
> 
Got it. mtk_wdt_init will be moved after watchdog_init_timeout in V2

BRs,
FreddyHsin

> >  	watchdog_init_timeout(&mtk_wdt->wdt_dev, timeout, dev);
> 
> just before initializing/setting the real timeout doesn't really make sense.
> 
> >  	watchdog_set_nowayout(&mtk_wdt->wdt_dev, nowayout);
> >  	watchdog_set_restart_priority(&mtk_wdt->wdt_dev, 128);
> >  
> > -	watchdog_set_drvdata(&mtk_wdt->wdt_dev, mtk_wdt);
> > -
> > -	mtk_wdt_stop(&mtk_wdt->wdt_dev);
> > -
> >  	watchdog_stop_on_reboot(&mtk_wdt->wdt_dev);
> >  	err = devm_watchdog_register_device(dev, &mtk_wdt->wdt_dev);
> >  	if (unlikely(err))
> > 
> 

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