linux-kernel - Re: [PATCH RFC] introduce pm_call() macro to get rid of most #ifdef CONFIG

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Date:	Tue, 4 Mar 2008 01:42:21 +0300
From:	Anton Vorontsov <cbouatmailru@...il.com>
To:	Pavel Machek <pavel@....cz>
Cc:	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org
Subject: Re: [PATCH RFC] introduce pm_call() macro to get rid of most
	#ifdef CONFIG_PM

On Mon, Mar 03, 2008 at 03:18:18PM +0100, Pavel Machek wrote:
> Hi!
> 
> > diff --git a/include/linux/pm.h b/include/linux/pm.h
> > index 015b735..6e0b9c2 100644
> > --- a/include/linux/pm.h
> > +++ b/include/linux/pm.h
> > @@ -114,6 +114,13 @@ typedef struct pm_message {
> >  	int event;
> >  } pm_message_t;
> >  
> > +#ifdef CONFIG_PM
> > +#define pm_call(x) (x)
> > +#else
> > +/* avoid `defined but not used' warning */
> > +#define pm_call(x) ((x) - 1 ? NULL : NULL)
> > +#endif /* CONFIG_PM */
> > +
> 
> This is evil. Maybe your gcc is smart enough to optimize this away,
> but I'm not sure mine is.

No problem. Let's use __maybe_unsed then, it gives the same effect.

- - - -
Subject: introduce pm_call() macro to get rid of most #ifdef CONFIG_PM

Currently drivers handle CONFIG_PM this way:

#ifdef CONFIG_PM
drv_suspend() {}
drv_resume() {}
#else
#define drv_suspend NULL
#define drv_resume NULL
#endif

struct driver drv = {
	.suspend = drv_suspend,
	.resume = drv_resume,
};

With this patch, the code above converts into:

__maybe_unused drv_suspend() {}
__maybe_unused drv_resume() {}

struct driver drv = {
	.suspend = pm_call(drv_suspend),
	.resume = pm_call(drv_resume),
};

GCC will optimize away suspend/resume calls if they're really
not used.

Signed-off-by: Anton Vorontsov <cbouatmailru@...il.com>
---
 include/linux/pm.h |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/include/linux/pm.h b/include/linux/pm.h
index 015b735..a3932c7 100644
--- a/include/linux/pm.h
+++ b/include/linux/pm.h
@@ -114,6 +114,12 @@ typedef struct pm_message {
 	int event;
 } pm_message_t;
 
+#ifdef CONFIG_PM
+#define pm_call(x) (x)
+#else
+#define pm_call(x) NULL
+#endif /* CONFIG_PM */
+
 /*
  * Several driver power state transitions are externally visible, affecting
  * the state of pending I/O queues and (for drivers that touch hardware)
-- 
1.5.4.3

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