linux-kernel - Re: [PATCH 1/2] IOMMU Identity Mapping Support: iommu_identity

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Message-ID: <20090618183405.GC19771@sequoia.sous-sol.org>
Date:	Thu, 18 Jun 2009 11:34:05 -0700
From:	Chris Wright <chrisw@...s-sol.org>
To:	"Yu, Fenghua" <fenghua.yu@...el.com>
Cc:	"'Chris Wright'" <chrisw@...s-sol.org>,
	"'David Woodhouse'" <dwmw2@...radead.org>,
	"'Linus Torvalds'" <torvalds@...ux-foundation.org>,
	"'Stephen Rothwell'" <sfr@...b.auug.org.au>,
	"'Andrew Morton'" <akpm@...ux-foundation.org>,
	"'Ingo Molnar'" <mingo@...e.hu>,
	"'Christopher Wright'" <chrisw@...hat.com>,
	"Kay, Allen M" <allen.m.kay@...el.com>,
	"'iommu'" <iommu@...ts.linux-foundation.org>,
	"'lkml'" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] IOMMU Identity Mapping Support:
	iommu_identity_mapping definition

* Yu, Fenghua (fenghua.yu@...el.com) wrote:
> >>
> >> The first patch defines iommu_identity_mapping varialbe which controls
> >the
> >> identity mapping code and is 0 by default.
> >
> >The only real difference between "pt" and "identity" is hardware support.
> >We should have a single value we don't have to tell users to do different
> >things depending on their hardware (they won't even know what they have)
> >to achieve the same result.
> 
> Technically keeping two separate options in base kernel might be clear and easy to understand. A distro might merge them together or have other usage model.

This pushes burden to distros and users for no obvious gain.  Just like
queued invalidation vs. register based invalidation...it's a hardware
detail that users don't really care that much about, they just care
about user visible functionality.

thanks,
-chris
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