Re: [PATCH 20/28] mfd: arizona: Remove #ifdef guards for PM related functions

[Lee Jones]

On Mon, 08 Aug 2022, Richard Fitzgerald wrote:

> On 08/08/2022 12:01, Paul Cercueil wrote:
> > 
> > 
> > Le lun., août 8 2022 at 11:43:31 +0100, Richard Fitzgerald
> > <rf@xxxxxxxxxxxxxxxxxxxxx> a écrit :
> > > On 08/08/2022 11:06, Paul Cercueil wrote:
> > > > Hi Richard,
> > > > 
> > > > Le lun., août 8 2022 at 10:53:54 +0100, Richard Fitzgerald
> > > > <rf@xxxxxxxxxxxxxxxxxxxxx> a écrit :
> > > > > On 07/08/2022 15:52, Paul Cercueil wrote:
> > > > > > Only export the arizona_pm_ops if CONFIG_PM is set, but leave the
> > > > > > suspend/resume functions (and related code) outside #ifdef guards.
> > > > > > 
> > > > > > If CONFIG_PM is not set, the arizona_pm_ops will be defined as
> > > > > > "static __maybe_unused", and the structure plus all the callbacks will
> > > > > > be automatically dropped by the compiler.
> > > > > > 
> > > > > > The advantage is then that these functions are now always compiled
> > > > > > independently of any Kconfig option, and thanks to that bugs and
> > > > > > regressions are easier to catch.
> > > > > > 
> > > > > > Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
> > > > > > Cc: patches@xxxxxxxxxxxxxxxxxxxxx
> > > > > > ---
> > > > > >   drivers/mfd/arizona-core.c | 21 +++++++++++----------
> > > > > >   drivers/mfd/arizona-i2c.c  |  2 +-
> > > > > >   drivers/mfd/arizona-spi.c  |  2 +-
> > > > > >   3 files changed, 13 insertions(+), 12 deletions(-)
> > > > > > 
> > > > > > diff --git a/drivers/mfd/arizona-core.c b/drivers/mfd/arizona-core.c
> > > > > > index cbf1dd90b70d..c1acc9521f83 100644
> > > > > > --- a/drivers/mfd/arizona-core.c
> > > > > > +++ b/drivers/mfd/arizona-core.c
> > > > > > @@ -480,7 +480,6 @@ static int
> > > > > > wm5102_clear_write_sequencer(struct arizona *arizona)
> > > > > >       return 0;
> > > > > >   }
> > > > > >   -#ifdef CONFIG_PM
> > > > > >   static int arizona_isolate_dcvdd(struct arizona *arizona)
> > > > > 
> > > > > __maybe_unused?
> > > > 
> > > > No need. The symbols are always referenced.
> > > > 
> > > > > >   {
> > > > > >       int ret;
> > > > > > @@ -742,9 +741,7 @@ static int
> > > > > > arizona_runtime_suspend(struct device *dev)
> > > > > 
> > > > > __maybe_unused?
> > > > > 
> > > > > >         return 0;
> > > > > >   }
> > > > > > -#endif
> > > > > >   -#ifdef CONFIG_PM_SLEEP
> > > > > >   static int arizona_suspend(struct device *dev)
> > > > > 
> > > > > __maybe_unused?
> > > > > 
> > > > > >   {
> > > > > >       struct arizona *arizona = dev_get_drvdata(dev);
> > > > > > @@ -784,17 +781,21 @@ static int arizona_resume(struct device *dev)
> > > > > 
> > > > > __maybe_unused?
> > > > > 
> > > > > >         return 0;
> > > > > >   }
> > > > > > -#endif
> > > > > >   +#ifndef CONFIG_PM
> > > > > > +static __maybe_unused
> > > > > > +#endif
> > > > > 
> > > > > No need to ifdef a __maybe_unused.
> > > > 
> > > > Yes, it is needed, because the symbol is conditionally exported. If
> > > 
> > > Why conditionally export it?
> > > 
> > > > !CONFIG_PM, we want the compiler to discard the dev_pm_ops
> > >  and all the
> > > > callbacks, hence the "static __maybe_unused". That's the same
> > > > trick used > in _EXPORT_DEV_PM_OPS().
> > > > 
> > > > (note that this patch is broken as it does not change the struct
> > > > name, in the !PM case, which causes conflicts with the .h. I'll
> > > > fix in v2)
> > > > 
> > > > > >   const struct dev_pm_ops arizona_pm_ops = {
> > > > > > -    SET_RUNTIME_PM_OPS(arizona_runtime_suspend,
> > > > > > -               arizona_runtime_resume,
> > > > > > -               NULL)
> > > > > > -    SET_SYSTEM_SLEEP_PM_OPS(arizona_suspend, arizona_resume)
> > > > > > -    SET_NOIRQ_SYSTEM_SLEEP_PM_OPS(arizona_suspend_noirq,
> > > > > > -                      arizona_resume_noirq)
> > > > > > +    RUNTIME_PM_OPS(arizona_runtime_suspend,
> > > > > > +               arizona_runtime_resume,
> > > > > > +               NULL)
> > > > > > +    SYSTEM_SLEEP_PM_OPS(arizona_suspend, arizona_resume)
> > > > > > +    NOIRQ_SYSTEM_SLEEP_PM_OPS(arizona_suspend_noirq,
> > > > > > +                  arizona_resume_noirq)
> > > > > >   };
> > > > > > +#ifdef CONFIG_PM
> > > > > >   EXPORT_SYMBOL_GPL(arizona_pm_ops);
> > > > > > +#endif
> > > > > 
> > > > > This ifdeffing is ugly. Why must the structure only be exported if
> > > > > CONFIG_PM is set?
> > > > 
> > > > So that all the PM code is garbage-collected by the compiler if
> > > > !CONFIG_PM.
> > > 
> > > The functions will be dropped if they are not referenced. That doesn't
> > > answer why the struct must not be exported.
> > > 
> > > What is the aim of omitting the struct export?
> > 
> > The functions are always referenced by the dev_pm_ops structure.
> > Omitting the struct export means that the struct can now be a "static
> > __maybe_unused" symbol in the !CONFIG_PM case, and everything related to
> > PM will be automatically removed by the compiler.
> > 
> > Otherwise, the symbol is exported as usual. The symbol being
> > conditionally exported is not a problem - the struct is always
> > referenced (as it should be) using the pm_sleep_ptr() or pm_ptr()
> > macros.
> > 
> > This is basically what EXPORT_SIMPLE_DEV_PM_OPS() does by the way.
> > 
> > Cheers,
> > -Paul
> > 
> Ok,
> Well ultimately it's up to Lee as the maintainer of the MFD subsystem.
> 
> But the open-coded #ifdef around "static __maybe_unused" is ugly, so if
> this is going to be a common pattern a new macro would be nice.

I like to avoid #ifery in C files wherever possible.

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