linux-kernel - Re: prevent swsusp with PAE

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Message-Id: <20060831160546.3309d745.rdunlap@xenotime.net>
Date:	Thu, 31 Aug 2006 16:05:46 -0700
From:	"Randy.Dunlap" <rdunlap@...otime.net>
To:	Pavel Machek <pavel@....cz>
Cc:	Andrew Morton <akpm@...l.org>, "Rafael J. Wysocki" <rjw@...k.pl>,
	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: prevent swsusp with PAE

On Fri, 1 Sep 2006 00:52:34 +0200 Pavel Machek wrote:

> On Thu 2006-08-31 15:48:28, Andrew Morton wrote:
> > On Fri, 1 Sep 2006 00:35:21 +0200
> > Pavel Machek <pavel@....cz> wrote:
> > 
> > > > > diff --git a/include/asm-i386/suspend.h b/include/asm-i386/suspend.h
> > > > > index 08be1e5..01cd812 100644
> > > > > --- a/include/asm-i386/suspend.h
> > > > > +++ b/include/asm-i386/suspend.h
> > > > > @@ -16,6 +16,15 @@ arch_prepare_suspend(void)
> > > > >  		printk(KERN_ERR "PSE is required for swsusp.\n");
> > > > >  		return -EPERM;
> > > > >  	}
> > > > > +
> > > > > +#ifdef CONFIG_X86_PAE
> > > > > +	printk(KERN_ERR "swsusp is incompatible with PAE.\n");
> > > > > +	/* This is actually instance of the same problem. We need
> > > > > +	   identity mapping self-contained in swsusp_pg_dir, and PAE
> > > > > +	   prevents that. Solution could be copied from x86_64. */
> > > > > +	return -EPERM;
> > > > > +#endif
> > > > > +
> > > > >  	return 0;
> > > > >  }
> > > > 
> > > > Why not do this in Kconfig??
> > > 
> > > Well, Kconfig does not provide natural place for comments, and
> > > disappearing config option is sure to confuse people. But of course I
> > > can do it.
> > 
> > It would be more conventional.
> 
> Well, I have very similar check few lines above, and this is both i386
> specific, so I slightly prefer to do it in the code, but...

If we can prevent a non-working build in Kconfig, that's what
we should do.

> > I think what this really points at is a weakness in the menuconfig/xconfig/etc
> > user interfaces.  It should be possible to navigate to the presently-disabled
> > config option and ask it "why can't I turn you on?".
> 
> Yes, but I'll still have users asking me "why I can't turn it on" ;-).

menuconfig and xconfig both have Help and Search that can aid
with that, but I would still use the "comment" keyword also.

---
~Randy
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