[Intel-gfx] [PATCH] drm/i915: Init PPGTT before context enable

[Chris Wilson]

On Wed, Jan 21, 2015 at 10:35:58AM +0100, Daniel Vetter wrote:
> On Tue, Jan 20, 2015 at 05:21:42PM +0000, David Woodhouse wrote:
> > Commit 82460d972 ("drm/i915: Rework ppgtt init to no require an aliasing
> > ppgtt") introduced a regression on Broadwell, triggering the following
> > IOMMU fault at startup:
> > 
> >   vgaarb: device changed decodes: PCI:0000:00:02.0,olddecodes=io+mem,decodes=io+mem:owns=io+mem
> >   dmar: DRHD: handling fault status reg 2
> >   dmar: DMAR:[DMA Write] Request device [00:02.0] fault addr 880000
> >   DMAR:[fault reason 23] Unknown
> >   fbcon: inteldrmfb (fb0) is primary device
> > 
> > Signed-off-by: David Woodhouse <David.Woodhouse at intel.com>
> > Cc: stable at vger.kernel.org
> 
> I sugggested this change to David after staring at the offending patch for
> a while. I have no idea and theory whatsoever why this would upset the gpu
> less than the other way round. But it seems to work. David promised to
> chase hw people a bit more to get a more meaningful answer.

The issue is likely the execution of the golden render state batch
concurrently with the flip over to ppgtt. The GPU throws a pagefault and
we get an ERROR reported.

http://patchwork.freedesktop.org/patch/38270/
http://patchwork.freedesktop.org/patch/38269/
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre