Re: [PATCH 00/49] iio: Tree wide switch from CONFIG_PM* to __maybe_unused etc.

From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Paul Cercueil <paul@crapouillou.net>,
	Jonathan Cameron <jic23@kernel.org>, <linux-iio@vger.kernel.org>,
	Lars-Peter Clausen <lars@metafoo.de>,
	"Alexandre Belloni" <alexandre.belloni@bootlin.com>,
	Anson Huang <anson.huang@nxp.com>,
	Brian Masney <masneyb@onstation.org>,
	Fabrice Gasnier <fabrice.gasnier@foss.st.com>,
	Hans de Goede <hdegoede@redhat.com>,
	"Heiko Stuebner" <heiko.stuebner@theobroma-systems.com>,
	Icenowy Zheng <icenowy@aosc.io>,
	Jonathan Albrieux <jonathan.albrieux@gmail.com>,
	"Krzysztof Kozlowski" <krzk@kernel.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	"Luca Weiss" <luca@z3ntu.xyz>,
	Ludovic Desroches <ludovic.desroches@microchip.com>,
	Manivannan Sadhasivam <mani@kernel.org>,
	Martijn Braam <martijn@brixit.nl>,
	Maslov Dmitry <maslovdmitry@seeed.cc>,
	Olivier Moysan <olivier.moysan@foss.st.com>,
	Stefan-Gabriel Mirea <stefan-gabriel.mirea@nxp.com>,
	Vaishnav M A <vaishnav@beagleboard.org>
Subject: Re: [PATCH 00/49] iio: Tree wide switch from CONFIG_PM* to __maybe_unused etc.
Date: Wed, 24 Nov 2021 10:11:13 +0000	[thread overview]
Message-ID: <20211124101113.000033c6@Huawei.com> (raw)
In-Reply-To: <CAK8P3a3qs8fb1cMLu9WsFQmtff05zrpfmV--QZQta4_-Nt=MpA@mail.gmail.com>

On Wed, 24 Nov 2021 08:29:40 +0100
Arnd Bergmann <arnd@arndb.de> wrote:

> On Tue, Nov 23, 2021 at 11:11 PM Paul Cercueil <paul@crapouillou.net> wrote:
> >
> > One word about the pm_ptr() macro. Right now it's defined as:
> >   #ifdef CONFIG_PM
> >   #define pm_ptr(_ptr) (_ptr)
> >   #else
> >   #define pm_ptr(_ptr) NULL
> >   #endif
> >
> > It could be possible to define it like this instead:
> >   #define pm_ptr(_ptr) PTR_IF(IS_ENABLED(CONFIG_PM), (_ptr))
> >
> > The difference is that if !CONFIG_PM, in the first case the (_ptr) is
> > not visible by the compiler and the __maybe_unused is required, while
> > in the second case the (_ptr) is always visible by the compiler, but
> > discarded as dead code. The reason we'd want that is the same reason we
> > use IS_ENABLED() instead of macro guards; and you wouldn't need the
> > __maybe_unused attribute anywhere.  
> 
> That sounds like a great idea. I see there are only 12 users of pm_ptr at
> the moment, so auditing all of these should not be a problem.
> 
> I gave it a brief look and found that we probably only need to fix
> drivers/net/ethernet/realtek/r8169_main.c if we change the definition.

Cool.  

> 
> > The problem then is that the SET_*_PM_OPS macros are defined
> > differently according to CONFIG_PM, so their definition would need to
> > be changed to use the (redefined) pm_ptr() macro and a corresponding
> > pm_sleep_ptr() macro. Unfortunately since the SET_*_PM_OPS macros are
> > used everywhere with code wrapped around #ifdef CONFIG_PM guards, it
> > wouldn't be easy to change them, and it would just be easier to
> > introduce new macros.  
> 
> Right, this is what we've discussed multiple times, and I think everyone
> agreed we should do this, but so far we could not come up with a name
> for the new macro, and changing the macro in place is not practical unless
> we change hundreds of drivers in the same way as the iio series first.

Nasty indeed and I'm not sure how scriptable either as lots of subtle variants
unfortunately.

I'm cynical - don't need a good name.  *_OPS2 works fine for me as long as
the docs are good. 

Jonathan

> 
>        Arnd