Re: [PATCH v2 04/10] pinctrl: intel: Switch to use DEFINE_NOIRQ_DEV_PM_OPS() helper

[Paul Cercueil <paul@crapouillou.net>]

Hi Andy,

Le mardi 18 juillet 2023 à 15:57 +0300, Andy Shevchenko a écrit :
> On Mon, Jul 17, 2023 at 10:56 PM Paul Cercueil <paul@crapouillou.net>
> wrote:
> > Le lundi 17 juillet 2023 à 22:33 +0300, Andy Shevchenko a écrit :
> > > On Mon, Jul 17, 2023 at 10:02 PM Paul Cercueil
> > > <paul@crapouillou.net>
> > > wrote:
> > > > Le lundi 17 juillet 2023 à 20:28 +0300, Andy Shevchenko a écrit
> > > > :
> 
> ...
> 
> > > > So the correct way to update this driver would be to have a
> > > > conditionally-exported dev_pm_ops structure:
> > > > 
> > > > EXPORT_GPL_DEV_PM_OPS(intel_pinctrl_pm_ops) = {
> > > >     NOIRQ_SYSTEM_SLEEP_PM_OPS(intel_pinctrl_suspend_noirq,
> > > > intel_pinctrl_resume_noirq),
> > > > };
> > > 
> > > This looks ugly. I didn't know that EXPORT*PM_OPS designed that
> > > way,
> > > but it seems pm.h in such case needs EXPORT for NOIRQ case as
> > > well.
> > 
> > It's designed so that when CONFIG_PM is disabled, the dev_pm_ops is
> > garbage-collected along with all its callbacks.
> > 
> > I know it looks ugly, but we already have 4 variants (regular,
> > namespace, GPL, namespace + GPL), if we start to add macros for
> > specific use-cases then it will become bloated really quick.
> 
> Maybe macros can be replaced / changed to make it scale?

If you have any ideas, then yes absolutely.

> 
> > And the "bloat" I'm trying to avoid here is the extreme expansion
> > of
> > the API which makes it hard for people not familiar to the code to
> > understand what should be used and how.
> 
> So far, based on the rest of the messages in the thread the
> EXPORT*PM_OPS() have the following issues:
> 1) do not scale (for variants with different scope we need new set of
> macros);
> 2) do not cover cases with pm_sleep_ptr();
> 3) export symbols in case when it's not needed.
> 
> Am I right?

I think that's right yes.

> 
> > > > Then your two callbacks can be "static" and without #ifdef
> > > > guards.
> > > > 
> > > > The resulting "intel_pinctrl_pm_ops" can be marked as "extern"
> > > > in
> > > > the
> > > > pinctrl-intel.h without any guards, as long as it is only
> > > > referenced
> > > > with the pm_ptr() macro.
> > > 
> > > I'm not sure I got this. Currently drivers do not have any
> > > guards.
> > > Moreover, the correct one for noirq is pm_sleep_ptr(), isn't it?
> > 
> > The EXPORT_*_DEV_PM_OPS() macros do export the "dev_pm_ops"
> > conditionally depending on CONFIG_PM. We could add variants that
> > export
> > it conditionally depending on CONFIG_PM_SLEEP, but we're back at
> > the
> > problem of adding bloat.
> 
> Exactly.
> 
> > You could use pm_sleep_ptr() indeed, with the existing macros, with
> > the
> > drawback that in the case where CONFIG_PM && !CONFIG_PM_SLEEP, the
> > dev_pm_ops + callbacks are compiled in but never referenced.
> 
> And exactly.
> 
> I don't think they are ready to use (in the current form). But let's
> see what we may do better here...

They were OK when Jonathan and myself were updating the IIO drivers -
but now they definitely show their limitations.

Cheers,
-Paul