linux-kernel - Re: [PATCH v2 04/10] pinctrl: intel: Switch to use DEFINE_NOIRQ_DEV_PM

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Message-ID: <d674ed791e4e7a71b671d1a66a03796cd6867fde.camel@crapouillou.net>
Date:   Tue, 18 Jul 2023 15:55:35 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Balsam CHIHI <bchihi@...libre.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-renesas-soc@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-pm@...r.kernel.org, Andy Shevchenko <andy@...nel.org>,
        Sean Wang <sean.wang@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Andrew Lunn <andrew@...n.ch>,
        Gregory Clement <gregory.clement@...tlin.com>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>
Subject: Re: [PATCH v2 04/10] pinctrl: intel: Switch to use
 DEFINE_NOIRQ_DEV_PM_OPS() helper

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@...pouillou.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@...pouillou.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