linux-kernel - Re: [PATCH 3/9] mfd: intel_soc_pmic: remove unnecessary CONFIG_PM

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Date:   Fri, 30 Oct 2020 22:22:42 +0800
From:   Coiby Xu <coiby.xu@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Lee Jones <lee.jones@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...el.com>,
        Andy Shevchenko <andy@...nel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/9] mfd: intel_soc_pmic: remove unnecessary
 CONFIG_PM_SLEEP

On Thu, Oct 29, 2020 at 07:04:44PM +0200, Andy Shevchenko wrote:
>On Thu, Oct 29, 2020 at 5:27 PM Lee Jones <lee.jones@...aro.org> wrote:
>> On Thu, 29 Oct 2020, Coiby Xu wrote:
>> > On Thu, Oct 29, 2020 at 01:00:29PM +0200, Andy Shevchenko wrote:
>> > > On Thu, Oct 29, 2020 at 06:06:41PM +0800, Coiby Xu wrote:
>> > > > SIMPLE_DEV_PM_OPS has already took good care of CONFIG_PM_CONFIG.
>> > >
>> > > Have you compiled this with
>> > >     % make W=1 ...
>> > > ?
>> > >
>> >
>> > Sorry my bad. I thought I had run "make modules" with CONFIG_PM_SLEEP
>> > disabled. I'll run "make W=1 M=..." for each driver after adding
>> > __maybe_unused in v2.
>>
>> No, thank you.  Just keep it as it is.
>>
>> The current code is space saving.
>
>Perhaps you need to go thru __maybe_unused handling.
>There are pros and cons of each approach, but not above.
>
Can you elaborate on the pros and cons of each approach? There's
convincing reason to prefer __maybe_unused over CONFIG_PM_SLEEP
according to Arnd Bergmann [1],

> > By and large, drivers handle this by using a CONFIG_PM_SLEEP ifdef.
> >
> > Unless you can make an extremely convincing argument why not to do
> > so here, I'd like you to handle it that way instead.
>
> [adding linux-pm to Cc]
>
> The main reason is that everyone gets the #ifdef wrong, I run into
> half a dozen new build regressions with linux-next every week on
> average, the typical problems being:
>
> - testing CONFIG_PM_SLEEP instead of CONFIG_PM, leading to an unused
>   function warning
> - testing CONFIG_PM instead of CONFIG_PM_SLEEP, leading to a build
>   failure
> - calling a function outside of the #ifdef only from inside an
>   otherwise correct #ifdef, again leading to an unused function
>   warning
> - causing a warning inside of the #ifdef but only testing if that
>   is disabled, leading to a problem if the macro is set (this is
>   rare these days for CONFIG_PM as that is normally enabled)
>
> Using __maybe_unused avoids all of the above.

You option is valuable to me because I'm making a tree-wide change.

Currently there are 929 drivers having device PM callbacks,

$ grep -rI "\.pm = &" --include=*.c  ./|wc -l
929

I put all files having device PM callbacks into four categories
based on weather a file has CONFIG_PM_SLEEP or PM macro like
SET_SYSTEM_SLEEP_PM_OPS, here are the statistics,
  1. have both CONFIG_PM_SLEEP and PM_OPS macro: 213
  2. have CONFIG_PM_SLEEP but no PM_OPS macro: 19
  3. have PM macro but not CONFIG_PM_SLEEP: 347
  4. no PM macro or CONFIG_PM_SLEEP: 302

[1] https://lore.kernel.org/patchwork/comment/919944/

>--
>With Best Regards,
>Andy Shevchenko

--
Best regards,
Coiby