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Date: Mon, 12 Jan 2009 22:12:30 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Harvey Harrison <harvey.harrison@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
       "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>,
       Torsten Kaiser <just.for.lkml@googlemail.com>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [git pull] x86 fixes
Message-ID: <20090112211230.GA7320@elte.hu>
References: <20090111143951.GA6666@elte.hu> <64bb37e0901110845o2561db4auf68b86d024d210a0@mail.gmail.com> <7E82351C108FA840AB1866AC776AEC4643BB73C5@orsmsx505.amr.corp.intel.com> <64bb37e0901121101y73c492fel38a70681f226b526@mail.gmail.com> <20090112191934.GA28851@linux-os.sc.intel.com> <20090112192912.GA31650@linux-os.sc.intel.com> <alpine.LFD.2.00.0901121145220.6528@localhost.localdomain> <20090112205259.GA5303@elte.hu> <1231794230.5405.1.camel@brick>
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* Harvey Harrison <harvey.harrison@gmail.com> wrote:

> On Mon, 2009-01-12 at 21:52 +0100, Ingo Molnar wrote:
> > * Linus Torvalds <torvalds@linux-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