Subject: Re: [RFC Patch] use MTRR for write combining if PAT is not
 available
From: Suresh Siddha <suresh.b.siddha@intel.com>
Reply-To: Suresh Siddha <suresh.b.siddha@intel.com>
To: Eric Anholt <eric@anholt.net>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>,
       Thomas Schlichter <thomas.schlichter@web.de>,
       Ingo Molnar <mingo@elte.hu>, Jan Beulich <JBeulich@novell.com>,
       Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>,
       Robert Hancock <hancockrwd@gmail.com>,
       Henrique de Moraes Holschuh <hmh@hmh.eng.br>,
       "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>,
       Tejun Heo <tj@kernel.org>, "x86@kernel.org" <x86@kernel.org>,
       Yinghai Lu <yinghai@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
       Arjan van de Ven <arjan@linux.intel.com>,
       "dri-devel@lists.sourceforge.net" <dri-devel@lists.sourceforge.net>,
       Ingo Molnar <mingo@redhat.com>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       Thomas Hellstrom <thellstrom@vmware.com>,
       "H. Peter Anvin" <hpa@zytor.com>
In-Reply-To: <1256262799.15120.8.camel@gaiman.anholt.net>
References: <1394846127@web.de>
	 <4ADF32A0020000780001B20A@vpn.id2.novell.com>
	 <20091021173514.GA32227@elte.hu>
	 <200910212201.36578.thomas.schlichter@web.de>
	 <1256205210.2530.28.camel@sbs-t61>
	 <1256225689.32075.6.camel@gaiman.anholt.net>
	 <1256248050.2546.9.camel@sbs-t61>  <20091023081047.4d8abc29@jbarnes-x200>
	 <1256256717.2534.6.camel@sbs-t61>
	 <1256262799.15120.8.camel@gaiman.anholt.net>
Content-Type: text/plain
Organization: Intel Corp
Date: Thu, 22 Oct 2009 21:33:21 -0700
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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@intel.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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