linux-kernel - Re: [PATCH 7/7] watchdog: s3c2410: Let kernel kick watchdog

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Message-ID: <CAPLW+4kphtac24fcpVUENAMUAdHp2fkzJ0N_r_63Soq6R2VZBg@mail.gmail.com>
Date:   Sat, 30 Oct 2021 17:29:44 +0300
From:   Sam Protsenko <semen.protsenko@...aro.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        linux-watchdog@...r.kernel.org,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Linux Samsung SOC <linux-samsung-soc@...r.kernel.org>
Subject: Re: [PATCH 7/7] watchdog: s3c2410: Let kernel kick watchdog

On Fri, 29 Oct 2021 at 03:30, Guenter Roeck <linux@...ck-us.net> wrote:
>
> On 10/28/21 11:35 AM, Sam Protsenko wrote:
> > When "tmr_atboot" module param is set, the watchdog is started in
> > driver's probe. In that case, also set WDOG_HW_RUNNING bit to let
> > watchdog core driver know it's running. This way wathcdog core can kick
> > the watchdog for us (if CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED option is
> > enabled), until user space takes control.
> >
> > Signed-off-by: Sam Protsenko <semen.protsenko@...aro.org>
> > ---
> >   drivers/watchdog/s3c2410_wdt.c | 26 +++++++++++++++-----------
> >   1 file changed, 15 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/watchdog/s3c2410_wdt.c b/drivers/watchdog/s3c2410_wdt.c
> > index ca082b1226e3..9af014ff1468 100644
> > --- a/drivers/watchdog/s3c2410_wdt.c
> > +++ b/drivers/watchdog/s3c2410_wdt.c
> > @@ -732,6 +732,21 @@ static int s3c2410wdt_probe(struct platform_device *pdev)
> >       wdt->wdt_device.bootstatus = s3c2410wdt_get_bootstatus(wdt);
> >       wdt->wdt_device.parent = dev;
> >
> > +     /*
> > +      * If "tmr_atboot" param is non-zero, start the watchdog right now. Also
> > +      * set WDOG_HW_RUNNING bit, so that watchdog core can kick the watchdog.
> > +      *
> > +      * If we're not enabling the watchdog, then ensure it is disabled if it
> > +      * has been left running from the bootloader or other source.
> > +      */
> > +     if (tmr_atboot && started == 0) {
> > +             dev_info(dev, "starting watchdog timer\n");
> > +             s3c2410wdt_start(&wdt->wdt_device);
> > +             set_bit(WDOG_HW_RUNNING, &wdt->wdt_device.status);
> > +     } else if (!tmr_atboot) {
> > +             s3c2410wdt_stop(&wdt->wdt_device);
> > +     }
> > +
>
> This doesn't cover the case where the watchdog is already enabled by the BIOS.
> In that case, WDOG_HW_RUNNING won't be set, and the watchdog will time out
> if the userspace handler is not loaded fast enough. The code should consistently
> set WDOG_HW_RUNNING if the watchdog is running.
>

As I understand, in the case when bootloader started the watchdog, the
driver just stops it. You can see it in the code you replied to.

    } else if (!tmr_atboot) {
            s3c2410wdt_stop(&wdt->wdt_device);

In other words, having "tmr_atboot" module param makes it irrelevant
whether bootloader enabled WDT or no.

> Guenter
>
> >       ret = watchdog_register_device(&wdt->wdt_device);
> >       if (ret)
> >               goto err_cpufreq;
> > @@ -740,17 +755,6 @@ static int s3c2410wdt_probe(struct platform_device *pdev)
> >       if (ret < 0)
> >               goto err_unregister;
> >
> > -     if (tmr_atboot && started == 0) {
> > -             dev_info(dev, "starting watchdog timer\n");
> > -             s3c2410wdt_start(&wdt->wdt_device);
> > -     } else if (!tmr_atboot) {
> > -             /* if we're not enabling the watchdog, then ensure it is
> > -              * disabled if it has been left running from the bootloader
> > -              * or other source */
> > -
> > -             s3c2410wdt_stop(&wdt->wdt_device);
> > -     }
> > -
> >       platform_set_drvdata(pdev, wdt);
> >
> >       /* print out a statement of readiness */
> >
>