[Intel-gfx] [2.6.32 PATCH] agp/intel-agp: Clear entire GTT on startup

[Eric Anholt]

On Wed, 02 Dec 2009 11:00:05 +0000, David Woodhouse <dwmw2 at infradead.org> wrote:
> Some BIOSes fail to initialise the GTT, which will cause DMA faults when
> the IOMMU is enabled. We need to clear the whole thing, not just the
> part that Linux is going to use.
> 
> Signed-off-by: David Woodhouse <David.Woodhouse at intel.com>
> ---
> 
> Without this, certain machines will see a lot of spurious DMA faults
> when the IOMMU is enabled. And since the CONFIG_DMAR_BROKEN_GFX_WA
> option to work around graphics drivers that don't use the PCI DMA API
> correctly has been removed in 2.6.32, it's probably worth merging this
> patch ASAP. After confirming that it's doing the right thing on i915 and
> (especially) G33, perhaps.

Applied to -next.  This is a really cool patch.  Our understanding was
that the GTT that the HW could reference was just the space referenced
by the PCI aperture.  If the GGTT is actually 2GB, that means that we
could put together support for 2GB address space without having to make
the jump to PPGTT all at once.  Many workloads would love this.
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