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

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Message-ID: <CAJZ5v0gZo=kvWWSOTzNaYohr1Yk0iiZnj3+WZbq+jK3HXLu16g@mail.gmail.com>
Date:   Mon, 9 Nov 2020 16:53:57 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        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, Nov 9, 2020 at 4:50 PM Ulf Hansson <ulf.hansson@...aro.org> wrote:
>
> 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?

It doesn't work this way, though.

The "get" happens even if the device has not been suspended.