[Bug 89467] [ivb gt2] GPU hangs in 4.0: where did my seqno writes go?

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89467

--- Comment #54 from Chris Wilson <chris at chris-wilson.co.uk> ---
I don't have a good explanation, but we may as well try punching a few things
and see what we can break:

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c
b/drivers/gpu/drm/i915/intel_ringbuffer.c
index e5b3c6dbd467..c972f24d50cc 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -1087,18 +1087,20 @@ gen6_add_request(struct intel_engine_cs *ring)
        int ret;

        if (ring->semaphore.signal)
-               ret = ring->semaphore.signal(ring, 4);
+               ret = ring->semaphore.signal(ring, 6);
        else
-               ret = intel_ring_begin(ring, 4);
+               ret = intel_ring_begin(ring, 6);

        if (ret)
                return ret;

+       intel_ring_emit(ring, MI_ARB_ON_OFF | MI_ARB_DISABLE);
        intel_ring_emit(ring, MI_STORE_DWORD_INDEX);
        intel_ring_emit(ring, I915_GEM_HWS_INDEX <<
MI_STORE_DWORD_INDEX_SHIFT);
        intel_ring_emit(ring,
                   
i915_gem_request_get_seqno(ring->outstanding_lazy_request));
        intel_ring_emit(ring, MI_USER_INTERRUPT);
+       intel_ring_emit(ring, MI_ARB_ON_OFF | MI_ARB_ENABLE);
        __intel_ring_advance(ring);

        return 0;

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