linux-kernel - Re: {Spam?} Re: [PATCH][RFC] Kill off legacy power management stuff.

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Message-Id: <200704181524.16980.lenb@kernel.org>
Date:	Wed, 18 Apr 2007 15:24:16 -0400
From:	Len Brown <lenb@...nel.org>
To:	"Robert P. J. Day" <rpjday@...dspring.com>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: {Spam?} Re: [PATCH][RFC] Kill off legacy power management stuff.

On Saturday 14 April 2007 09:01, Robert P. J. Day wrote:
> On Fri, 13 Apr 2007, Stephen Rothwell wrote:
> 
> > On Fri, 13 Apr 2007 04:20:10 -0400 (EDT) "Robert P. J. Day" <rpjday@...dspring.com> wrote:
> > >
> > > On Fri, 13 Apr 2007, Stephen Rothwell wrote:
> > > >
> > > > One thing that comes to mind is that you will need some way to
> > > > make sure that only one of ACPI and APM get initialized ...
> > >
> > > i don't see how that has anything to do with removing legacy PM
> > > support.  you can select both ACPI and APM *now*.  if that's a bad
> > > thing, then fixing it is a completely independent issue.
> >
> > Except your patch removes this hunk:
> >
> > @@ -2264,14 +2248,6 @@ static int __init apm_init(void)
> >  		apm_info.disabled = 1;
> >  		return -ENODEV;
> >  	}
> > -	if (PM_IS_ACTIVE()) {
> > -		printk(KERN_NOTICE "apm: overridden by ACPI.\n");
> > -		apm_info.disabled = 1;
> > -		return -ENODEV;
> > -	}
> > -#ifdef CONFIG_PM_LEGACY
> > -	pm_active = 1;
> > -#endif
> >
> > in apm.c and a similar piece of the ACPI initialisation that
> > prevented one initialising if the other had already initialised.
> 
> ah, just took a closer look at this.  from <linux/pm_legacy.h>:
> ...
> #ifdef CONFIG_PM_LEGACY
> ...
> #else
> #define PM_IS_ACTIVE() 0
> ...
> #endif
> 
> so if you choose not to configure legacy PM, that macro equates to
> false and that "if" construct in arch/i386/kernel/apm.c doesn't come
> into play, anyway.
> 
> so i re-iterate what i posted in my earlier e-mail -- if APM and ACPI
> want to avoid clashing, they have to do it without invoking anything
> related to legacy PM.

Here is how it should work.
CONFIG_ACPI and CONFIG_APM should both available in a kernel build.
However, at boot time, of ACPI is active, then APM should be disabled.

The pm_active flag used to handle this, but that method was BROKEN
when the CONFIG_PM_LEGACY #define was added.  Today, there are systems
(such as the Thinkpad T30) that will not boot if CONFIG_PM_LEGACY
is not defined.  The reason nobody is complaining is because the distros
are currently defining CONFIG_PM_LEGACY.  But when you nuke that option
and everything under it, this bug will be exposed and some systems will stop booting.

-Len
-
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