linux-kernel - RE: [PATCH 2/2]Add Variable Page Size and IA64 Support in Intel IOMMU: IA64 Specific Part

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Date:	Sat, 04 Oct 2008 07:09:57 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	"Yu, Fenghua" <fenghua.yu@...el.com>
Cc:	Bjorn Helgaas <bjorn.helgaas@...com>,
	"Luck, Tony" <tony.luck@...el.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Ingo Molnar <mingo@...e.hu>, Avi Kivity <avi@...hat.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>
Subject: RE: [PATCH 2/2]Add Variable Page Size and IA64 Support in Intel
	IOMMU: IA64 Specific Part

On Fri, 2008-10-03 at 17:53 -0700, Yu, Fenghua wrote:
> >Architecturally, I'm surprised that ia64 would need to actually do a
> >cache flush.  I would think the VT-d hardware would do coherent
> accesses which would make the cache flush unnecessary.
> 
> VT-d hardware supports both non cache coherency and cache coherency by
> bit Coherency in Extended Capabilities Register.

But is the version without the cache coherency actually going to be
_seen_ on IA64?

> Could you please point me to the doc that explicitly says that
> architecturally ia64 doesn't need cache flush?

For safety, we can always make the driver just refuse to initialise on
IA64 if the cache coherency bit isn't set.

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@...el.com                              Intel Corporation

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