Message-ID: <CAJZ5v0hJvsuOTj5j-0Jn-c9TPnbm70wPvdBkop2hRrdweoncDg@mail.gmail.com>
Date: Thu, 18 Sep 2025 22:41:32 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Takashi Iwai <tiwai@...e.de>
Cc: linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: PM runtime auto-cleanup macros

On Thu, Sep 18, 2025 at 10:19 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Thu, Sep 18, 2025 at 1:28 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
> >
> > On Thu, Sep 18, 2025 at 9:10 AM Takashi Iwai <tiwai@...e.de> wrote:
> > >
> > > On Wed, 17 Sep 2025 20:58:36 +0200,
> > > Rafael J. Wysocki wrote:
> > > >
> > > > Hi,
> > > >
> > > > Sorry for the delay.
> > > >
> > > > On Thu, Sep 11, 2025 at 9:31 AM Takashi Iwai <tiwai@...e.de> wrote:
> > > > >
> > > > > On Wed, 10 Sep 2025 16:00:17 +0200,
> > > > > Takashi Iwai wrote:
> > > > > >
> > > > > > Hi,
> > > > > >
> > > > > > while I worked on the code cleanups in the drivers with the recent
> > > > > > auto-cleanup macros, I noticed that pm_runtime_get*() and _put*() can
> > > > > > be also managed with the auto-cleanup gracefully, too.  Actually we
> > > > > > already defined the __free(pm_runtime_put) in commit bfa4477751e9, and
> > > > > > there is a (single) user of it in pci-sysfs.c.
> > > > > >
> > > > > > Now I wanted to extend it to pm_runtime_put_autosuspend() as:
> > > > > >
> > > > > > DEFINE_FREE(pm_runtime_put_autosuspend, struct device *,
> > > > > >            if (_T) pm_runtime_put_autosuspend(_T))
> > > > > >
> > > > > > Then one can use it like
> > > > > >
> > > > > >       ret = pm_runtime_resume_and_get(dev);
> > > > > >       if (ret < 0)
> > > > > >               return ret;
> > > > > >       struct device *pmdev __free(pm_runtime_put_autosuspend) = dev;
> > > > > >
> > > > > > that is similar as done in pci-sysfs.c.  So far, so good.
> > > > > >
> > > > > > But, I find putting the line like above at each place a bit ugly.
> > > > > > So I'm wondering whether it'd be better to introduce some helper
> > > > > > macros, e.g.
> > > > > >
> > > > > > #define pm_runtime_auto_clean(dev, var) \
> > > > > >       struct device *var __free(pm_runtime_put) = (dev)
> > > > >
> > > > > It can be even simpler by assigning a temporary variable such as:
> > > > >
> > > > > #define pm_runtime_auto_clean(dev) \
> > > > >         struct device *__pm_runtime_var ## __LINE__ __free(pm_runtime_put) = (dev)
> > > >
> > > > Well, if there's something like
> > > >
> > > > struct device *pm_runtime_resume_and_get_dev(struct device *dev)
> > > > {
> > > >         int ret = pm_runtime_resume_and_get(dev);
> > > >         if (ret < 0)
> > > >                 return ERR_PTR(ret);
> > > >
> > > >         return dev;
> > > > }
> > > >
> > > > It would be a matter of redefining the FREE to also take error
> > > > pointers into account and you could do
> > > >
> > > > struct device *__dev __free(pm_runtim_put) = pm_runtime_resume_and_get_dev(dev);
> > > > if (IS_ERR(__dev))
> > > >         return PTR_ERR(__dev);
> > >
> > > That'll work, too.  Though, I find the notion of __free() and a
> > > temporary variable __dev a bit too cumbersome; it's used only for
> > > auto-clean stuff, so it could be somewhat anonymous.
> >
> > No, it is not used only for auto-clean, it is also used for return
> > value checking and it represents a reference on the original dev.  It
> > cannot be entirely anonymous because of the error checking part.
> >
> > The point is that this is one statement instead of two and so it is
> > arguably harder to mess up with.
> >
> > > But it's all about a matter of taste, and I'd follow what you and
> > > other guys suggest.
> > >
> > > FWIW, there are lots of code doing like
> > >
> > >         pm_runtime_get_sync(dev);
> > >         mutex_lock(&foo);
> > >         ....
> > >         mutex_unlock(&foo);
> > >         pm_runtime_put(dev);
> > >         return;
> > >
> > > or
> > >
> > >         ret = pm_runtime_resume_and_get(dev);
> > >         if (ret)
> > >                 return ret;
> > >         mutex_lock(&foo);
> > >         ....
> > >         mutex_unlock(&foo);
> > >         pm_runtime_put_autosuspend(dev);
> > >         return 0;
> > >
> > > and they can be converted nicely with guard() once when PM runtime can
> > > be automatically unreferenced.  With my proposed change, it would
> > > become like:
> > >
> > >         pm_runtime_get_sync(dev);
> > >         pm_runtime_auto_clean(dev);
> >
> > For the case in which the pm_runtime_get_sync() return value is
> > discarded, you could define a guard and do
> >
> > guard(pm_runtime_get_sync)(dev);
> >
> > here.
> >
> > The case checking the return value is less straightforward.
> >
> > >         guard(mutex)(&foo);
> > >         ....
> > >         return;
> > >
> > > or
> > >
> > >         ret = pm_runtime_resume_and_get(dev);
> > >         if (ret)
> > >                 return ret;
> > >         pm_runtime_auto_clean_autosuspend(dev);
> > >         guard(mutex)(&foo);
> > >         ....
> > >         return 0;
> > >
>
> I guess what I'm saying means basically something like this:
>
> DEFINE_CLASS(pm_runtime_resume_and_get, struct device *,
>          if (!IS_ERR_OR_NULL(_T)) pm_tuntime_put(_T),
> pm_runtime_resume_and_get_dev(dev), struct device *dev)
>
> DEFINE_CLASS(pm_runtime_resume_and_get_auto, struct device *,
>          if (!IS_ERR_OR_NULL(_T)) pm_tuntime_put_autosuspend(_T),
> pm_runtime_resume_and_get_dev(dev), struct device *dev)
>
> and analogously for pm_runtime_get_sync().

And it kind of makes sense either.  Do

CLASS(pm_runtime_resume_and_get, active_dev)(dev);
if (IS_ERR(active_dev))
        return PTR_ERR(active_dev);

and now use active_dev for representing the device until it gets out
of the scope.

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