[Intel-gfx] [PATCH] drm/i915: Fill unused GGTT with scratch pages for VT-d

[Chris Wilson]

On Tue, Jul 12, 2016 at 11:50:26AM +0300, Joonas Lahtinen wrote:
> On pe, 2016-06-24 at 14:07 +0100, Chris Wilson wrote:
> > One of the numerous VT-d workarounds we require is that the display
> > hardware reads past the end of the buffer triggering VT-d faults. This
> > is acknowledged in the code as being safe "since we fill the unused
> > portions of the GGTT with the scratch page". Alas, that is no longer
> > always true and so we trigger DMAR read faults.
> > 
> > Skylake also requires another workaround to avoid mixing VT-d and
> > unpopulated PTE, and so there we also need to ensure we fill unused
> > entries with the scratch page.
> 
> Rather agressive W/A for just scanout, so maybe drop the scanout word?

The original w/a was just for VT'd + scanout, I was thinking of a
comment, but it never materialised.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre