linux-kernel - Re: [git pull] x86 fixes

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Date:	Mon, 12 Jan 2009 22:12:30 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Harvey Harrison <harvey.harrison@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Torsten Kaiser <just.for.lkml@...glemail.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [git pull] x86 fixes


* Harvey Harrison <harvey.harrison@...il.com> wrote:

> On Mon, 2009-01-12 at 21:52 +0100, Ingo Molnar wrote:
> > * Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> > +static inline int is_new_memtype_allowed(unsigned long flags,
> > +                                               unsigned long new_flags)
> > +{
> > +       /*
> > +        * Certain new memtypes are not allowed with certain
> > +        * requested memtype:
> > +        * - request is uncached, return cannot be write-back
> > +        * - request is write-combine, return cannot be write-back
> > +        */
> > +       if ((flags == _PAGE_CACHE_UC_MINUS &&
> > +            new_flags == _PAGE_CACHE_WB) ||
> > +           (flags == _PAGE_CACHE_WC &&
> > +            new_flags == _PAGE_CACHE_WB)) {
> > +               return 0;
> > +       }
> 
> 	if ((flags == _PAGE_CACHE_UC_MINUS || flags == _PAGE_CACHE_WC) &&
> 	    (new_flags == _PAGE_CACHE_WB))
> 
> might be a bit neater perhaps.

indeed. The most readable one is probably:

static inline int
is_new_memtype_allowed(unsigned long flags, unsigned long new_flags)
{
	/*
	 * Certain new memtypes are not allowed with certain
	 * requested memtype:
	 * - request is uncached, return cannot be write-back
	 * - request is write-combine, return cannot be write-back
	 */

	if (new_flags != _PAGE_CACHE_WB)
		return 1;

	if (flags == _PAGE_CACHE_UC_MINUS)
		return 0;
	if (flags == _PAGE_CACHE_WC)
		return 0;

	return 1;
}

	Ingo
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