linux-kernel - Re: [RFC Patch] use MTRR for write combining if PAT is not available

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Date:	Fri, 23 Oct 2009 08:10:47 +0900
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	Eric Anholt <eric@...olt.net>,
	Thomas Schlichter <thomas.schlichter@....de>,
	Ingo Molnar <mingo@...e.hu>, Jan Beulich <JBeulich@...ell.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Robert Hancock <hancockrwd@...il.com>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Tejun Heo <tj@...nel.org>, "x86@...nel.org" <x86@...nel.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	"dri-devel@...ts.sourceforge.net" <dri-devel@...ts.sourceforge.net>,
	Ingo Molnar <mingo@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Hellstrom <thellstrom@...are.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC Patch] use MTRR for write combining if PAT is not
 available

On Thu, 22 Oct 2009 14:47:30 -0700
Suresh Siddha <suresh.b.siddha@...el.com> wrote:

> On Thu, 2009-10-22 at 08:34 -0700, Eric Anholt wrote:
> > Can we just not create the _wc sysfs entry if we don't have PAT?  I
> > don't think there's userland relying on its presence as opposed to
> > the non-_wc entry.
> 
> Yes indeed. Jesse do you see an issue with this? This is simple and
> clean. Thanks Eric.

Yeah, I think that will be fine.  In fact, older versions of
libpciaccess will behave better if we do it that way (iirc it only
allocates an MTRR if the resource_wc file doesn't exist or fails to get
mapped).

Jesse
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