linux-kernel - Re: [PATCH 2/5] PM: core: Redefine pm

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Message-ID: <20211216111021.7b3eaada@jic23-huawei>
Date:   Thu, 16 Dec 2021 11:10:21 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     "Rafael J . Wysocki" <rafael@...nel.org>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Arnd Bergmann <arnd@...db.de>, list@...ndingux.net,
        linux-mips@...r.kernel.org, linux-mmc@...r.kernel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH 2/5] PM: core: Redefine pm_ptr() macro

On Tue,  7 Dec 2021 00:20:59 +0000
Paul Cercueil <paul@...pouillou.net> wrote:

> The pm_ptr() macro was previously conditionally defined, according to
> the value of the CONFIG_PM option. This meant that the pointed structure
> was either referenced (if CONFIG_PM was set), or never referenced (if
> CONFIG_PM was not set), causing it to be detected as unused by the
> compiler.
> 
> This worked fine, but required the __maybe_unused compiler attribute to
> be used to every symbol pointed to by a pointer wrapped with pm_ptr().
> 
> We can do better. With this change, the pm_ptr() is now defined the
> same, independently of the value of CONFIG_PM. It now uses the (?:)
> ternary operator to conditionally resolve to its argument. Since the
> condition is known at compile time, the compiler will then choose to
> discard the unused symbols, which won't need to be tagged with
> __maybe_unused anymore.
> 
> This pm_ptr() macro is usually used with pointers to dev_pm_ops
> structures created with SIMPLE_DEV_PM_OPS() or similar macros. These do
> use a __maybe_unused flag, which is now useless with this change, so it
> later can be removed. However in the meantime it causes no harm, and all
> the drivers still compile fine with the new pm_ptr() macro.
> 
> Signed-off-by: Paul Cercueil <paul@...pouillou.net>

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>

> ---
>  include/linux/pm.h | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/include/linux/pm.h b/include/linux/pm.h
> index 1d8209c09686..b88ac7dcf2a2 100644
> --- a/include/linux/pm.h
> +++ b/include/linux/pm.h
> @@ -373,11 +373,7 @@ const struct dev_pm_ops __maybe_unused name = { \
>  	SET_RUNTIME_PM_OPS(suspend_fn, resume_fn, idle_fn) \
>  }
>  
> -#ifdef CONFIG_PM
> -#define pm_ptr(_ptr) (_ptr)
> -#else
> -#define pm_ptr(_ptr) NULL
> -#endif
> +#define pm_ptr(_ptr) PTR_IF(IS_ENABLED(CONFIG_PM), (_ptr))
>  
>  /*
>   * PM_EVENT_ messages