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

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Date:	Wed, 21 Oct 2009 15:11:12 +0100
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	"Thomas Schlichter" <thomas.schlichter@....de>
Cc:	"Jeremy Fitzhardinge" <jeremy.fitzhardinge@...rix.com>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Robert Hancock" <hancockrwd@...il.com>,
	"Henrique de Moraes Holschuh" <hmh@....eng.br>,
	"Suresh Siddha" <suresh.b.siddha@...el.com>,
	"Venkatesh Pallipadi" <venkatesh.pallipadi@...el.com>,
	"Tejun Heo" <tj@...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>,
	"Ingo Molnar" <mingo@...hat.com>, <linux-kernel@...r.kernel.org>,
	<jbarnes@...tuousgeek.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

>>> Thomas Schlichter <thomas.schlichter@....de> 21.10.09 15:45 >>>
>Ingo Molnar wrote:
>> Can we eliminate mtrr_add_unaligned() as Suresh suggested, and still 
>> make it work on your testbox?
>
>Yes, I had that in the first place, but Jan suggested to extend it to also
>handle non-aligned, non-power-of-two cases:
>  http://marc.info/?l=linux-kernel&m=125541951529918&w=2 

I merely pointed out it wouldn't work for unaligned addresses or sizes
passed in.

>So if it's OK for Jan, I'll reduce the functionality again and use mtrr_add()
>instead. Btw. this simply means to drop mtrr_add_unaligned(), all the other
>parts are still required for reference counting and a proper mtrr_del() on file
>close.

I'm perfectly fine with just handling the aligned case, as long as the code
checks that the alignment constraints are met.

Jan

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