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In-Reply-To: <20190117211410.GA30749@anatevka>
From:   Guenter Roeck <groeck@google.com>
Date:   Thu, 17 Jan 2019 13:16:51 -0800
Message-ID: <CABXOdTefAMjNypoa9uB2nMgAwi_e1pRMRxiDbXGfGT8_v7Ho-Q@mail.gmail.com>
Subject: Re: [PATCHv2] watchdog: qcom: Add suspend/resume support
To:     Jerry.Hoemann@hpe.com
Cc:     Stephen Boyd <swboyd@chromium.org>,
        Guenter Roeck <groeck@chromium.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>,
        Wim Van Sebroeck <wim@linux-watchdog.org>,
        linux-watchdog@vger.kernel.org,
        Rajendra Nayak <rnayak@codeaurora.org>,
        Vivek Gautam <vivek.gautam@codeaurora.org>,
        Sibi Sankar <sibis@codeaurora.org>,
        Doug Anderson <dianders@chromium.org>,
        linux-arm-kernel@lists.infradead.org,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-arm-msm@vger.kernel.org
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On Thu, Jan 17, 2019 at 1:14 PM Jerry Hoemann <jerry.hoemann@hpe.com> wrote:
>
> On Thu, Jan 17, 2019 at 11:09:31AM -0800, Guenter Roeck wrote:
> > On Thu, Jan 17, 2019 at 10:37 AM Stephen Boyd <swboyd@chromium.org> wrote:
> > >
> > > Quoting Sai Prakash Ranjan (2019-01-17 07:19:42)
> > > > diff --git a/drivers/watchdog/qcom-wdt.c b/drivers/watchdog/qcom-wdt.c
> > > > index 780971318810..5dfd604477a4 100644
> > > > --- a/drivers/watchdog/qcom-wdt.c
> > > > +++ b/drivers/watchdog/qcom-wdt.c
> > > > @@ -245,6 +245,28 @@ static int qcom_wdt_remove(struct platform_device *pdev)
> > > >         return 0;
> > > >  }
> > > >
> > > > +static int __maybe_unused qcom_wdt_suspend(struct device *dev)
> > > > +{
> > > > +       struct qcom_wdt *wdt = dev_get_drvdata(dev);
> > > > +
> > > > +       if (watchdog_active(&wdt->wdd))
> > > > +               qcom_wdt_stop(&wdt->wdd);
> > > > +
> > > > +       return 0;
> > > > +}
> > > > +
> > > > +static int __maybe_unused qcom_wdt_resume(struct device *dev)
> > > > +{
> > > > +       struct qcom_wdt *wdt = dev_get_drvdata(dev);
> > > > +
> > > > +       if (watchdog_active(&wdt->wdd))
> > > > +               qcom_wdt_start(&wdt->wdd);
> > > > +
> > > > +       return 0;
> > > > +}
> > >
> > > This looks fairly generic. For example, the Mediatek driver also stops
> > > and starts (but also pings after starting). Grepping for 'active' in
> > > drivers/watchdog/ finds more examples. Could there be some functions in
> > > watchdog core that do the common things like watchdog_stop() and
> > > watchdog_start() and watchdog_start_and_ping()? Or maybe a bit can be
> > > set during registration so that the 'struct class watchdog_class' can
> > > get PM ops to stop and start on suspend/resume of the watchdog character
> > > device?
> > >
> > > Nothing is wrong with the patch, I'm just bemoaning the amount of code
> > > duplication here.
> > >
> >
> > Patch(es) to add the functionality to the watchdog core are welcome;
> > it should be possible to move the functionality into the core (maybe
> > to be enabled with a new watchdog API call). Doing it using the class
> > device sounds like an excellent idea. This should be straightforward
> > to implement, though the question of "should we ping on resume or not"
> > might be an endless source for bike shedding fun.
> >
> > Guenter
>
> It could be controlled by a currently unused bit in the
> watchdog_info.options.  Then people can agree to disagree.
>
I thought about that, but that would result in inconsistent behavior
across drivers. Of course we could be all fancy and make it runtime
configurable via ioctl.

Guenter