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Date:   Sat, 31 Oct 2020 13:12:51 +0100
From:   Robert Marko <robert.marko@...tura.hr>
To:     kathirav@...eaurora.org
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        wim@...ux-watchdog.org, linux@...ck-us.net,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] watchdog: qcom_wdt: set WDOG_HW_RUNNING bit when appropriate

On Fri, Oct 30, 2020 at 6:21 AM <kathirav@...eaurora.org> wrote:
>
> On 2020-10-28 17:16, Robert Marko wrote:
> > If the watchdog hardware is enabled/running during boot, e.g.
> > due to a boot loader configuring it, we must tell the
> > watchdog framework about this fact so that it can ping the
> > watchdog until userspace opens the device and takes over
> > control.
> >
> > Do so using the WDOG_HW_RUNNING flag that exists for exactly
> > that use-case.
> >
> > Given the watchdog driver core doesn't know what timeout was
> > originally set by whoever started the watchdog (boot loader),
> > we make sure to update the timeout in the hardware according
> > to what the watchdog core thinks it is.
> >
> > Signed-off-by: Robert Marko <robert.marko@...tura.hr>
> > Cc: Luka Perkov <luka.perkov@...tura.hr>
> > ---
> > Changes in v2:
> > * Correct authorship
> >
> >  drivers/watchdog/qcom-wdt.c | 22 ++++++++++++++++++++++
> >  1 file changed, 22 insertions(+)
> >
> > diff --git a/drivers/watchdog/qcom-wdt.c b/drivers/watchdog/qcom-wdt.c
> > index ab7465d186fd..28c93a918e38 100644
> > --- a/drivers/watchdog/qcom-wdt.c
> > +++ b/drivers/watchdog/qcom-wdt.c
> > @@ -152,6 +152,13 @@ static int qcom_wdt_restart(struct
> > watchdog_device *wdd, unsigned long action,
> >       return 0;
> >  }
> >
> > +static int qcom_wdt_is_running(struct watchdog_device *wdd)
> > +{
> > +     struct qcom_wdt *wdt = to_qcom_wdt(wdd);
> > +
> > +     return (readl(wdt_addr(wdt, WDT_EN)) & 1);
>
> QCOM_WDT_ENABLE macro can be used instead of 1?
Yes, pushed this in v4(Forgot to do it in v3).
Thanks
>
> > +}
> > +
> >  static const struct watchdog_ops qcom_wdt_ops = {
> >       .start          = qcom_wdt_start,
> >       .stop           = qcom_wdt_stop,
> > @@ -294,6 +301,21 @@ static int qcom_wdt_probe(struct platform_device
> > *pdev)
> >       wdt->wdd.timeout = min(wdt->wdd.max_timeout, 30U);
> >       watchdog_init_timeout(&wdt->wdd, 0, dev);
> >
> > +     if (qcom_wdt_is_running(&wdt->wdd)) {
> > +             /*
> > +              * Make sure to apply timeout from watchdog core, taking
> > +              * the prescaler of this driver here into account (the
> > +              * boot loader might be using a different prescaler).
> > +              *
> > +              * To avoid spurious resets because of different scaling,
> > +              * we first disable the watchdog, set the new prescaler
> > +              * and timeout, and then re-enable the watchdog.
> > +              */
> > +             qcom_wdt_stop(&wdt->wdd);
>
> qcom_wdt_start disables the WDT, configure the timeout values and
> enables it. Do we still need to call qcom_wdt_stop?
No, as the start will actually stop the WDT and then set everything up.
Pushed in v3.
>
> > +             qcom_wdt_start(&wdt->wdd);
> > +             set_bit(WDOG_HW_RUNNING, &wdt->wdd.status);
> > +     }
> > +
> >       ret = devm_watchdog_register_device(dev, &wdt->wdd);
> >       if (ret)
> >               return ret;

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