linux-kernel - Re: [PATCH 3/9] add frontend implementation for the IOMMU API

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Message-Id: <20081201173830B.fujita.tomonori@lab.ntt.co.jp>
Date:	Mon, 1 Dec 2008 17:38:11 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	joerg.roedel@....com
Cc:	fujita.tomonori@....ntt.co.jp, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
	weidong.han@...el.com, mingo@...hat.com, avi@...hat.com,
	amit.shah@...hat.com
Subject: Re: [PATCH 3/9] add frontend implementation for the IOMMU API

On Fri, 28 Nov 2008 12:31:29 +0100
Joerg Roedel <joerg.roedel@....com> wrote:

> On Fri, Nov 28, 2008 at 06:40:41PM +0900, FUJITA Tomonori wrote:
> > On Thu, 27 Nov 2008 16:40:48 +0100
> > Joerg Roedel <joerg.roedel@....com> wrote:
> > 
> > > Signed-off-by: Joerg Roedel <joerg.roedel@....com>
> > > ---
> > >  drivers/base/iommu.c |   94 ++++++++++++++++++++++++++++++++++++++++++++++++++
> > >  1 files changed, 94 insertions(+), 0 deletions(-)
> > >  create mode 100644 drivers/base/iommu.c
> > > 
> > > diff --git a/drivers/base/iommu.c b/drivers/base/iommu.c
> > > new file mode 100644
> > > index 0000000..7250b9c
> > > --- /dev/null
> > > +++ b/drivers/base/iommu.c
> > 
> > Hmm, why is this at drivers/base/? Anyone except for kvm could use
> > this? If so, under virt/ is more appropriate?
> 
> I don't see a reason why this should be KVM specific. KVM is the only
> user for now. But it can be used for i.e. UIO too. Or in drivers to
> speed up devices which have bad performance when they do scather gather
> IO.

If there are some except for kvm that could use this, it should be
fine, I guess.

Can you add such information (e.g. who could use this) to the patch
description? It should be in the git log if the patch is merged.


> > The majority of the names (include/linux/iommu.h, iommu.c, iommu_ops,
> > etc) looks too generic? We already have lots of similar things
> > (e.g. arch/{x86,ia64}/asm/iommu.h, several archs' iommu.c, etc). Such
> > names are expected to be used by all the IOMMUs.
> 
> The API is already useful for more than KVM. I also plan to extend it to
> support more types of IOMMUs than VT-d and AMD IOMMU in the future. But
> these changes are more intrusive than this patchset and need more
> discussion. I prefer to do small steps into this direction.

Can you be more specific? What IOMMU could use this? For example, how
GART can use this? I think that people expect the name 'struct
iommu_ops' to be an abstract for all the IOMMUs (or the majority at
least). If this works like that, the name is a good choice, I think.
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