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

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Message-Id: <1256272401.2569.6.camel@sbs-t61>
Date:	Thu, 22 Oct 2009 21:33:21 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	Eric Anholt <eric@...olt.net>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	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, 2009-10-22 at 18:53 -0700, Eric Anholt wrote:
> On Thu, 2009-10-22 at 17:11 -0700, Suresh Siddha wrote:
> > On Thu, 2009-10-22 at 16:10 -0700, Jesse Barnes wrote:
> > > 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).
> > 
> > Eric, care to send the patch?
> 
> I don't have a patch, I was just suggesting a way to handle the
> submitter's problem that won't involve complicated changes that nobody
> else will be testing since everyone *should* have a graphics driver for
> their graphics hardware.

I can send the patch early next week unless Thomas or someone else beats
me.

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