linux-kernel - Re: linux-next: build warnings after merge of the char-misc tree

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Message-Id: <1481d53e-9fe3-4605-8776-587a44fdc0ce@app.fastmail.com>
Date:   Mon, 14 Nov 2022 10:16:53 +0100
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Liu Ying" <victor.liu@....com>,
        "Stephen Rothwell" <sfr@...b.auug.org.au>,
        "Greg KH" <greg@...ah.com>
Cc:     "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        linux-next <linux-next@...r.kernel.org>
Subject: Re: linux-next: build warnings after merge of the char-misc tree

On Mon, Nov 14, 2022, at 10:03, Liu Ying wrote:
> On Mon, 2022-11-14 at 08:33 +0100, Arnd Bergmann wrote:
>> On Mon, Nov 14, 2022, at 08:17, Stephen Rothwell wrote:
>> > Hi all,
>> > 
>> > After merging the char-misc tree, today's linux-next build (powerpc
>> > allnoconfig) produced these warnings:
>> > 
>> > drivers/bus/simple-pm-bus.c:96:12: warning: 
>> > 'simple_pm_bus_runtime_resume' defined but not used [-Wunused-function]
>> >    96 | static int simple_pm_bus_runtime_resume(struct device *dev)
>> >       |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> > drivers/bus/simple-pm-bus.c:87:12: warning: 
>> > 'simple_pm_bus_runtime_suspend' defined but not used [-Wunused-function]
>> >    87 | static int simple_pm_bus_runtime_suspend(struct device *dev)
>> >       |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> > 
>> > Introduced by commit
>> > 
>> >   882cf4c913d7 ("drivers: bus: simple-pm-bus: Use clocks")
>> 
>> I see that this is caused by the patch using the old-style
>> SET_RUNTIME_PM_OPS/SET_NOIRQ_SYSTEM_SLEEP_PM_OPS macros
>> instead of the correct SYSTEM_SLEEP_PM_OPS/NOIRQ_SYSTEM_SLEEP_PM_OPS
>> versions.
>> 
>
> You meant RUNTIME_PM_OPS/NOIRQ_SYSTEM_SLEEP_PM_OPS macros should be
> used, right?

Right, sorry for mixing up the runtime ones.

> Why not add __maybe_unused to the callbacks like below snippet instead?
> This way, the old-style macros may determine those callbacks are NULL
> or non-NULL according to CONFIG_PM_SLEEP and CONFIG_PM.

That was the old way of doing it before 1a3c7bb08826 ("PM: core: Add
new *_PM_OPS macros, deprecate old ones"), we are slowly moving to
the new ones instead to avoid having to add __maybe_unused annotations.

You may however want to use ".pm = pm_ptr(&simple_pm_bus_pm_ops)" if
you care about the space savings for configurations with CONFIG_PM
disabled.

      Arnd