drm/i915: Stop overwriting RING_IMR in rcs resume

We store the engine->imr mask and set up the RING_IMR register on
restarting the engine. We do not then want to overwrite it with
an incomplete mask later as we may then lose interrupts!
Reported-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190418132720.3716-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -873,9 +873,6 @@ static int init_render_ring(struct intel_engine_cs *engine)
 	if (IS_GEN_RANGE(dev_priv, 6, 7))
 		I915_WRITE(INSTPM, _MASKED_BIT_ENABLE(INSTPM_FORCE_ORDERING));
 
-	if (INTEL_GEN(dev_priv) >= 6)
-		ENGINE_WRITE(engine, RING_IMR, ~engine->irq_keep_mask);
-
 	return 0;
 }