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

From: Paul Cercueil <paul@crapouillou.net>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Jonathan Cameron <jic23@kernel.org>,
	linux-iio@vger.kernel.org, Lars-Peter Clausen <lars@metafoo.de>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	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: Sun, 28 Nov 2021 12:30:41 +0000	[thread overview]
Message-ID: <538A3R.42M33QXSDK222@crapouillou.net> (raw)
In-Reply-To: <CAK8P3a2znndSzP8L+OS=uayC7sNoOEnp8bqM8bmUqk-ptMy62A@mail.gmail.com>

Hi,

Le dim., nov. 28 2021 at 10:26:40 +0100, Arnd Bergmann <arnd@arndb.de> 
a écrit :
> On Sat, Nov 27, 2021 at 7:02 PM Jonathan Cameron <jic23@kernel.org> 
> wrote:
>>  On Tue, 23 Nov 2021 22:11:08 +0000 Paul Cercueil 
>> <paul@crapouillou.net> wrote:
> ?
>>  > 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.
>> 
>>  Small question here.  Why would these macros need to use pm_ptr() 
>> macro at all?
>> 
>>  Why not just stop them being conditional on CONFIG_PM at all and 
>> let dead
>>  code removal kill them off for us?  You might want to do something 
>> different
>>  for the CONFIG_PM_SLEEP ones though if we care about having it that 
>> fine
>>  grained.
> 
> Agreed, there is no need to use pm_ptr() inside of the new macros, it 
> would just
> be convenient to define them this way.

In that case all the callbacks of a dev_pm_ops will be compiled even 
though .suspend/.resume are only for CONFIG_PM_SLEEP.

The driver could do:
.dev.pm = pm_sleep_ptr(&my_pm_sleep_ops),

But that means the driver's dev needs to be aware that pm_sleep_ptr() 
is for simple PM, and pm_ptr() if runtime PM is used.

The alternative I suggested was to use pm_sleep_ptr() inside the 
SET_*_PM_OPS macros (and not pm_ptr() which wouldn't make much sense, I 
agree) so that the callbacks would be included only when 
CONFIG_PM_SLEEP is set; and the drivers would only ever use pm_ptr() 
for their .dev.pm.

I'm slightly in favor of the first solution, just because it would make 
the kernel smaller if !CONFIG_PM_SLEEP as you wouldn't have an empty 
dev_pm_ops struct.

Cheers,
-Paul