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 17:40:23 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     zhangqilong <zhangqilong3@...wei.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "fugang.duan@....com" <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 5:15 PM zhangqilong <zhangqilong3@...wei.com> wrote:
>
> Hi
>
> >
> > On Mon, Nov 9, 2020 at 4:50 PM zhangqilong <zhangqilong3@...wei.com>
> > wrote:
> > >
> > > > operation to deal with usage counter
> > > >
> > > > 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/20200520
> > > > > 0951 48.10995-1-dinghao.liu@....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."
> > > >
> > >
> > > How about the following description.
> > > /**
> > > 390  * pm_runtime_general_get - Bump up usage counter of a device and
> > resume it.
> > > 391  * @dev: Target device.
> > > 392  *
> > > 393  * Increase runtime PM usage counter of @dev first, and carry out
> > > runtime-resume
> > > 394  * of it synchronously. If __pm_runtime_resume return negative
> > > value(device is in
> > > 395  * error state), we to need decrease the usage counter before it
> > > return. If
> > > 396  * __pm_runtime_resume return positive value, it means the runtime
> > > of device has
> > > 397  * already been in active state, and we let the new wrapper return zero
> > instead.
> > > 398  *
> >
> > If you add the paragraph below, the one above becomes redundant IMV.
> >
> > > 399  * Resume @dev synchronously and if that is successful, and
> > > increment its runtime
> >
> > "Resume @dev synchronously and if that is successful, increment its runtime"
> >
> > (drop the extra "and").
> >
> > > 400  * PM usage counter if it turn out to equal to 0. The runtime PM
> > > usage counter of
> >
> > The "if it turn out to equal to 0" phrase is redundant (and the grammar in it is
> > incorrect).
> >
> > > 401  * @dev has been incremented or a negative error code otherwise.
> > > 402  */
> >
> > Why don't you use what I said verbatim?
>
> I had misunderstand just now, sorry for that. The description is as follows:
> 389 /**
> 390  * pm_runtime_resume_and_get - Bump up usage counter of a device and resume it.
> 391  * @dev: Target device.
> 392  *
> 393  * Resume @dev synchronously if that is successful, increment its runtime PM

"Resume @dev synchronously and if that is successful, increment its runtime PM"

(missing "and").

> 394  * usage counter.  Return 0 if the runtime PM usage counter of @dev has been
> 395  * incremented or a negative error code otherwise.
> 396  */
>
> Do you think it's OK?

Apart from the above typo, yes it is.

Thanks!