netdev - Re: [PATCH v2 1/2] PM: runtime: Add a general runtime get sync operation to deal with usage counter

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Date:   Mon, 9 Nov 2020 16:49:45 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Zhang Qilong <zhangqilong3@...wei.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Fugang Duan <fugang.duan@....com>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] PM: runtime: Add a general runtime get sync
 operation to deal with usage counter

On Mon, 9 Nov 2020 at 16:20, Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Mon, Nov 9, 2020 at 4:00 PM Zhang Qilong <zhangqilong3@...wei.com> wrote:
> >
> > In many case, we need to check return value of pm_runtime_get_sync, but
> > it brings a trouble to the usage counter processing. Many callers forget
> > to decrease the usage counter when it failed. It has been discussed a
> > lot[0][1]. So we add a function to deal with the usage counter for better
> > coding.
> >
> > [0]https://lkml.org/lkml/2020/6/14/88
> > [1]https://patchwork.ozlabs.org/project/linux-tegra/patch/20200520095148.10995-1-dinghao.liu@zju.edu.cn/
> > Signed-off-by: Zhang Qilong <zhangqilong3@...wei.com>
> > ---
> >  include/linux/pm_runtime.h | 30 ++++++++++++++++++++++++++++++
> >  1 file changed, 30 insertions(+)
> >
> > diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h
> > index 4b708f4e8eed..6549ce764400 100644
> > --- a/include/linux/pm_runtime.h
> > +++ b/include/linux/pm_runtime.h
> > @@ -386,6 +386,36 @@ static inline int pm_runtime_get_sync(struct device *dev)
> >         return __pm_runtime_resume(dev, RPM_GET_PUT);
> >  }
> >
> > +/**
> > + * pm_runtime_general_get - Bump up usage counter of a device and resume it.
> > + * @dev: Target device.
> > + *
> > + * Increase runtime PM usage counter of @dev first, and carry out runtime-resume
> > + * of it synchronously. If __pm_runtime_resume return negative value(device is in
> > + * error state), we to need decrease the usage counter before it return. If
> > + * __pm_runtime_resume return positive value, it means the runtime of device has
> > + * already been in active state, and we let the new wrapper return zero instead.
> > + *
> > + * The possible return values of this function is zero or negative value.
> > + * zero:
> > + *    - it means resume succeeed or runtime of device has already been active, the
> > + *      runtime PM usage counter of @dev remains incremented.
> > + * negative:
> > + *    - it means failure and the runtime PM usage counter of @dev has been balanced.
>
> The kerneldoc above is kind of noisy and it is hard to figure out what
> the helper really does from it.
>
> You could basically say something like "Resume @dev synchronously and
> if that is successful, increment its runtime PM usage counter.  Return
> 0 if the runtime PM usage counter of @dev has been incremented or a
> negative error code otherwise."
>
> > + */
> > +static inline int pm_runtime_general_get(struct device *dev)
>
> What about pm_runtime_resume_and_get()?

We already have pm_runtime_get_if_active() - so perhaps
pm_runtime_get_if_suspended() could be an option as well?

>
> > +{
> > +       int ret = 0;
>
> This extra initialization is not necessary.
>
> You can initialize ret to the __pm_runtime_resume() return value right away.
>
> > +
> > +       ret = __pm_runtime_resume(dev, RPM_GET_PUT);
> > +       if (ret < 0) {
> > +               pm_runtime_put_noidle(dev);
> > +               return ret;
> > +       }
> > +
> > +       return 0;
> > +}
> > +
> >  /**
> >   * pm_runtime_put - Drop device usage counter and queue up "idle check" if 0.
> >   * @dev: Target device.
> > --

Kind regards
Uffe