linux-kernel - Re: [RFC/PATCH 1/3] pm: make PM macros more smart

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Message-ID: <20131220195527.GA25927@amd.pavel.ucw.cz>
Date:	Fri, 20 Dec 2013 20:55:27 +0100
From:	Pavel Machek <pavel@....cz>
To:	David Cohen <david.a.cohen@...ux.intel.com>
Cc:	rjw@...ysocki.net, len.brown@...el.com,
	sarah.a.sharp@...ux.intel.com, gregkh@...uxfoundation.org,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org, santosh.shilimkar@...com
Subject: Re: [RFC/PATCH 1/3] pm: make PM macros more smart

On Sun 2013-12-15 11:25:08, David Cohen wrote:
> On Sun, Dec 15, 2013 at 06:51:12PM +0100, Pavel Machek wrote:
> > On Thu 2013-12-12 21:18:23, David Cohen wrote:
> > > This patch makes SET_SYSTEM_SLEEP_PM_OPS() and SET_RUNTIME_PM_OPS() more
> > > smart.
> > > 
> > > Despite those macros check for '#ifdef CONFIG_PM_SLEEP/RUNTIME' to avoid
> > > setting the callbacks when such #ifdef's aren't defined, they don't
> > > handle compiler to avoid messages like that:
> > > 
> > > drivers/usb/host/xhci-plat.c:200:12: warning: ???xhci_plat_suspend??? defined but not used [-Wunused-function]
> > > drivers/usb/host/xhci-plat.c:208:12: warning: ???xhci_plat_resume??? defined but not used [-Wunused-function]
> > > 
> > > As result, those macros get rid of #ifdef's when setting callbacks but
> > > not when implementing them.
> > > 
> > > With this patch, drivers using SET_*_PM_OPS() macros don't need to #ifdef
> > > the callbacks implementation as well.
> > 
> > Well... Interesting trickery, but it means that resulting kernel
> > will be bigge due to the dead functions no?
> 
> Actually, it doesn't get bigger. Before sending the patch I did this
> dummy test app:
> 
> --------------------------------------------------------------------------------
> #include <stdio.h>
> 
> #define USE_IT_OR_LOOSE_IT(fn)  ((void *)((unsigned long)(fn) - (unsigned long)(fn)))
> 
> #ifdef MAKE_ME_NULL
> static int func1(int a)
> {
>         printf("Hey!!\n");
>         return 0;
> }
> #endif

I thought that point of this patch series was getting rid of the
#ifdefs around the function...? Now I'm confused.

> struct global_data {
>         int (*func)(int);
> };
> 
> static struct global_data gd = {
> #ifdef MAKE_ME_NULL
>         .func = USE_IT_OR_LOOSE_IT(func1),

If you have ifdef around the function, why do you need magic here? Why
not

	.func = func1

?

Basically the warning tells you that you want the ifdef around the
function, too... (Otherwise you waste space). That seems like good
warning.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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