Re: [PATCHv2 4/5] watchdog: rti-wdt: attach to running watchdog during probe

[Tero Kristo]

On 05/07/2020 18:07, Guenter Roeck wrote:
> On 7/3/20 5:04 AM, Tero Kristo wrote:
> > If the RTI watchdog is running already during probe, the driver must
> > configure itself to match the HW. Window size and timeout is probed from
> > hardware, and the last keepalive ping is adjusted to match it also.
> >
> > Signed-off-by: Tero Kristo <t-kristo@xxxxxx>
> > ---
> >   drivers/watchdog/rti_wdt.c | 26 +++++++++++++++++++++++---
> >   1 file changed, 23 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/watchdog/rti_wdt.c b/drivers/watchdog/rti_wdt.c
> > index 110bfc8d0bb3..987e5a798cb4 100644
> > --- a/drivers/watchdog/rti_wdt.c
> > +++ b/drivers/watchdog/rti_wdt.c
> > @@ -213,6 +213,7 @@ static int rti_wdt_probe(struct platform_device *pdev)
> >   	struct watchdog_device *wdd;
> >   	struct rti_wdt_device *wdt;
> >   	struct clk *clk;
> > +	u32 last_ping = 0;
> >   
> >   	wdt = devm_kzalloc(dev, sizeof(*wdt), GFP_KERNEL);
> >   	if (!wdt)
> > @@ -258,11 +259,8 @@ static int rti_wdt_probe(struct platform_device *pdev)
> >   	wdd->min_timeout = 1;
> >   	wdd->max_hw_heartbeat_ms = (WDT_PRELOAD_MAX << WDT_PRELOAD_SHIFT) /
> >   		wdt->freq * 1000;
> > -	wdd->timeout = DEFAULT_HEARTBEAT;
>
> What if the watchdog is not running ?

Configuring wdd->timeout seems redundant, it gets set by the 
watchdog_init_timeout call done later. I just moved that post the check 
for a running watchdog so that the same call is used for both cases.

> >   	wdd->parent = dev;
> >   
> > -	watchdog_init_timeout(wdd, heartbeat, dev);
> > -
> >   	watchdog_set_drvdata(wdd, wdt);
> >   	watchdog_set_nowayout(wdd, 1);
> >   	watchdog_set_restart_priority(wdd, 128);
> > @@ -274,12 +272,34 @@ static int rti_wdt_probe(struct platform_device *pdev)
> >   		goto err_iomap;
> >   	}
> >   
> > +	if (readl(wdt->base + RTIDWDCTRL) == WDENABLE_KEY) {
> > +		u32 time_left;
> > +
> > +		set_bit(WDOG_HW_RUNNING, &wdd->status);
> > +		time_left = rti_wdt_get_timeleft(wdd);
> > +		heartbeat = readl(wdt->base + RTIDWDPRLD);
> > +		heartbeat <<= WDT_PRELOAD_SHIFT;
> > +		heartbeat /= wdt->freq;
> > +
>
> This ignores any heartbeat configured as module parameter, which most
> people will consider unexpected. It might be worthwhile documenting that.

I'll add a dev_warn for this case.

> > +		wsize = readl(wdt->base + RTIWWDSIZECTRL);
> > +		ret = rti_wdt_setup_hw_hb(wdd);
> > +		if (ret)
> > +			goto err_iomap;
> > +
> > +		last_ping = -(time_left - heartbeat) * 1000;
>
> Why the double negation ?
>
> 		last_ping = (heartbeat - time_left) * 1000;
>
> seems simpler. Also, what if heartbeat - time_left is negative for whatever
> reason ?

Will fix. I'll add a dev_warn for that case and assume last ping to be zero.

> I am not sure if it is a good idea to call rti_wdt_get_timeleft()
> here. It might be better to add a helper function such as
> rti_wdt_get_timeleft_ms() to return the time left in milli-seconds
> for improved accuracy.

Will add that.

-Tero

> > +	}
> > +
> > +	watchdog_init_timeout(wdd, heartbeat, dev);
> > +
> >   	ret = watchdog_register_device(wdd);
> >   	if (ret) {
> >   		dev_err(dev, "cannot register watchdog device\n");
> >   		goto err_iomap;
> >   	}
> >   
> > +	if (last_ping)
> > +		watchdog_set_last_hw_keepalive(wdd, last_ping);
> > +
> >   	return 0;
> >   
> >   err_iomap:

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