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

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Message-Id: <IVYYKQ.T5GFS8Z1QTP2@crapouillou.net>
Date:   Mon, 07 Dec 2020 12:33:18 +0000
From:   Paul Cercueil <paul@...pouillou.net>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        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 ARM <linux-arm-kernel@...ts.infradead.org>,
        ARM/Mediatek SoC support <linux-mediatek@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH] mmc: mediatek: mark PM functions as __maybe_unused

Hi Arnd,

Le ven. 4 déc. 2020 à 15:14, Arnd Bergmann <arnd@...nel.org> a écrit 
:
> 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)

By the way, as I'm ending up doing the same in a different context, I 
think it would be useful to have a IF_ENABLED() macro defined like this:

#define IF_ENABLED(_cfg, _ptr) (IS_ENABLED(_cfg) ? (_ptr) : NULL)

Then the pm_ptr(_ptr) macro could be defined like this:

#define pm_ptr(_ptr) IF_ENABLED(CONFIG_PM, _ptr)

Cheers,
-Paul

> 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