linux-kernel - Re: [PATCH] mmc: mediatek: mark PM functions as __maybe

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Date:   Fri, 4 Dec 2020 15:14:29 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Chaotian Jing <chaotian.jing@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Wenbin Mei <wenbin.mei@...iatek.com>,
        Arnd Bergmann <arnd@...db.de>,
        Chun-Hung Wu <chun-hung.wu@...iatek.com>,
        yong mao <yong.mao@...iatek.com>,
        Amey Narkhede <ameynarkhede03@...il.com>,
        Marek Vasut <marex@...x.de>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Paul Cercueil <paul@...pouillou.net>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH] mmc: mediatek: mark PM functions as __maybe_unused

On Fri, Dec 4, 2020 at 11:02 AM Ulf Hansson <ulf.hansson@...aro.org> wrote:
> On Thu, 3 Dec 2020 at 23:29, Arnd Bergmann <arnd@...nel.org> wrote:

> > -#ifdef CONFIG_PM
> >  static void msdc_save_reg(struct msdc_host *host)
>
> Shouldn't msdc_save|restore_reg() be turned into "__maybe_unused" as well?

There is no need since the compiler can figure that out already when there
is a reference to the function from dead code.

> >
> > -static int msdc_resume(struct device *dev)
> > +static int __maybe_unused msdc_resume(struct device *dev)
> >  {
> >         return pm_runtime_force_resume(dev);
> >  }
> > -#endif
> >
> >  static const struct dev_pm_ops msdc_dev_pm_ops = {
>
> You may also change this to a __maybe_unused, as long as you also
> assign the .pm pointer in the mt_msdc_driver with
> pm_ptr(&msdc_dev_pm_ops).
>
> Ideally the compiler should drop these functions/datas entirely then.

I don't see a lot of other instances of that yet, and it's fairly new.
Maybe we should fix it before it gets propagated further.

I would suggest we redefine pm_ptr like

#define pm_ptr(_ptr) (IS_ENABLED(CONFIG_PM) ? (_ptr) : NULL)

and remove the __maybe_unused annotations on those that we
already have. This also has the effect of dropping the unused
data from the object, but without having to an an #ifdef or
__maybe_unused.

Adding Paul and Rafael to Cc for clarification on this.

       Arnd