Re: [PATCH 2/2] pm: allow drivers to drop #ifdef and __maybe_unused from pm callbacks

[Masahiro Yamada <masahiroy@xxxxxxxxxx>]

On Fri, Apr 9, 2021 at 6:30 AM Arnd Bergmann <arnd@xxxxxxxx> wrote:
>
> On Thu, Apr 8, 2021 at 11:00 PM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote:
> >
> > Drivers typically surround suspend and resume callbacks with #ifdef
> > CONFIG_PM(_SLEEP) or mark them as __maybe_unused in order to avoid
> > -Wunused-const-variable warnings.
> >
> > With this commit, drivers will be able to remove #ifdef CONFIG_PM(_SLEEP)
> > and __maybe_unsed because unused functions are dropped by the compiler
> > instead of the preprocessor.
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
>
> I tried this before and could not get it to work right.
>
> >
> > -#ifdef CONFIG_PM_SLEEP
> > +#define pm_ptr(_ptr)           PTR_IF(IS_ENABLED(CONFIG_PM), _ptr)
> > +#define pm_sleep_ptr(_ptr)     PTR_IF(IS_ENABLED(CONFIG_PM_SLEEP), _ptr)
> > +
> >  #define SET_SYSTEM_SLEEP_PM_OPS(suspend_fn, resume_fn) \
> > -       .suspend = suspend_fn, \
> > -       .resume = resume_fn, \
> > -       .freeze = suspend_fn, \
> > -       .thaw = resume_fn, \
> > -       .poweroff = suspend_fn, \
> > -       .restore = resume_fn,
> > -#else
> > -#define SET_SYSTEM_SLEEP_PM_OPS(suspend_fn, resume_fn)
> > -#endif
> > +       .suspend  = pm_sleep_ptr(suspend_fn), \
> > +       .resume   = pm_sleep_ptr(resume_fn), \
> > +       .freeze   = pm_sleep_ptr(suspend_fn), \
> > +       .thaw     = pm_sleep_ptr(resume_fn), \
> > +       .poweroff = pm_sleep_ptr(suspend_fn), \
> > +       .restore  = pm_sleep_ptr(resume_fn),
>
> The problem that I think you inevitably hit is that you run into a missing
> declaration for any driver that still uses an #ifdef around a static
> function.
>
> The only way I can see us doing this is to create a new set of
> macros that behave like the version you propose here but leave
> the old macros in place until the last such #ifdef has been removed.
>
>        Arnd

Agh, you are right.
We cannot change all the callsites atomically due to the huge amount of users.

-- 
Best Regards
Masahiro Yamada