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

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Date:	Fri, 23 Oct 2009 09:24:54 +0200
From:	Thomas Schlichter <thomas.schlichter@....de>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Eric Anholt <eric@...olt.net>,
	Thomas Hellstrom <thellstrom@...are.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jan Beulich <JBeulich@...ell.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Tejun Heo <tj@...nel.org>,
	"dri-devel@...ts.sourceforge.net" <dri-devel@...ts.sourceforge.net>,
	Yinghai Lu <yinghai@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	Robert Hancock <hancockrwd@...il.com>
Subject: Re: [RFC Patch] use MTRR for write combining if PAT is not available

Suresh Siddha wrote:
> On Thu, 2009-10-22 at 21:31 -0700, Jesse Barnes wrote:
> > Here's a quick & dirty version, totally untested.  A cleaner approach
> > would be to separate the WC mapping routines and hide the return
> > -EINVAL in arch specific code...
> 
> Jesse How about this patch? Doing this in x86 is cleaner.
> 
> I would like Acks/sign-offs-by Thomas, Eric and Jesse, if it is ok with
> this patch and works.

Hmm, at this point I already was more than a week ago:
  http://marc.info/?l=linux-kernel&m=125537770514713&w=2

OK, I also modified ioremap() and set_memory_wc() but your patch is just part 
of what I did there...

And Eric Anholt answered:
> Seems like we should install an MTRR instead.  Requiring userland to set
> up the MTRR on the kernel's behalf is backwards.

Where I totally agree with him.

Regards,
  Thomas
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