Disable Intel IOMMU by default in kernel-3.1.5-7

[Josh Boyer]

On Sat, Dec 17, 2011 at 7:54 AM, Joshua C. <joshuacov at googlemail.com> wrote:
> I saw in the change log for the kernel-3.1.5-7 that the Intel IOMMU
> has been disabled by default. Can someone explain this decision or
> point me to the right discussion on the internet?

Dave or Matthew can answer more fully than I can, but there is an
on-going patch series to reenable Sandybridge GPU power savings and
DMAR conflicts with it some how.  I don't recall the details, but you
can find them in the discussions between Matthew and Keith Packard on
LKML.

Defaulting this to on has caused a number of odd issues in the past,
and it is mostly used by people using VT-d to assign physical
resources directly to virtual guests.  Those doing that can still boot
with intel_iommu=on.

josh