linux-kernel - Re: 3.6-rc7 boot crash + bisection

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Message-ID: <20120926151044.GE10549@amd.com>
Date:	Wed, 26 Sep 2012 17:10:44 +0200
From:	"Roedel, Joerg" <Joerg.Roedel@....com>
To:	Alex Williamson <alex.williamson@...hat.com>
CC:	Florian Dazinger <florian@...inger.net>,
	<linux-kernel@...r.kernel.org>,
	iommu <iommu@...ts.linux-foundation.org>
Subject: Re: 3.6-rc7 boot crash + bisection

On Wed, Sep 26, 2012 at 08:35:59AM -0600, Alex Williamson wrote:
> Hmm, that throws a kink in iommu groups.  So perhaps we need to make an
> alias interface to iommu groups.  Seems like this could just be an extra
> parameter to iommu_group_get and iommu_group_add_device (empty in the
> typical case).  Then we have the problem of what's the type for an
> alias?  For AMI-Vi, it's a u16, but we need to be more generic than
> that.  Maybe iommu groups should just treat it as a void* so iommus can
> use a pointer to some structure or a fixed value like a u16 bus:slot.
> Thoughts?

Good question. The iommu-groups are part of the IOMMU-API, with an
interface to the IOMMU drivers and one to the users of IOMMU-API. So the
alias handling itself should be a function of the interface to the IOMMU
driver. In general the interface should not be bus specific.

So a void pointer seems the only logical choice then. But I would not
limit its scope to alias handling. How about making it a bus-private
pointer where IOMMU driver store bus-specific information. That way we
make sure that there is one struct per bus-type for this pointer, and
not one structure per IOMMU driver.

	Joerg

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