[Intel-gfx] [PATCH] drm/i915: Protect gen7 irq_seqno_barrier with uncore lock

[Chris Wilson]

On Wed, Apr 27, 2016 at 09:02:01AM +0100, Chris Wilson wrote:
> Faced with sporadic machine hangs on gen7, that mimic the issue of
> concurrent writes to the same cacheline and seem to start with
> commit 9b9ed309 (drm/i915: Remove forcewake dance from seqno/irq
> barrier on legacy gen6+), let us restore the spinlock around the mmio
> read.
> 
> Fixes: 9b9ed3093613288247a27a55a6dd07f1222150f1
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala at intel.com>

Testcase: igt/gem_concurrent_blit #crw

I haven't been able to narrow this down to a simpler scenario. Still not
happy that I understand how we are triggering the erratum with this
read, but that does appear to be the case.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre