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

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Date:	Mon, 19 Oct 2009 09:36:18 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Thomas Schlichter <thomas.schlichter@....de>
Cc:	Jan Beulich <JBeulich@...ell.com>,
	Thomas Hellstrom <thellstrom@...are.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Arjan van de Ven <arjan@...ux.intel.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, jbarnes@...tuousgeek.org,
	Ingo Molnar <mingo@...hat.com>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Tejun Heo <tj@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	dri-devel@...ts.sourceforge.net, Yinghai Lu <yinghai@...nel.org>,
	Robert Hancock <hancockrwd@...il.com>
Subject: Re: [RFC Patch] use MTRR for write combining if PAT is not
	available

> X.org uses libpciaccess which tries to mmap with write combining enabled via
> /sys/bus/pci/devices/*/resource0_wc. Currently, when PAT is not enabled, we
> fall back to uncached mmap. Then libpciaccess thinks it succeeded mapping
> with write combining anabled and does not set up suited MTRR entries. ;-(

I am not familiar with libpciaccess, but I was wondering why that library
cannot realize it failed in its endeavour and use other means to accomplish
its goals?

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