drm/i915: fix render pipe control notify on sandybridge

This one is missed in last pipe control fix for sandybridge,
that really unmask interrupt bit for notify in render engine IMR.

Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_irq.c

@@ -1381,12 +1381,17 @@ static int ironlake_irq_postinstall(struct drm_device *dev)
 	I915_WRITE(DEIER, dev_priv->de_irq_enable_reg);
 	(void) I915_READ(DEIER);
 
-	/* user interrupt should be enabled, but masked initial */
+	/* Gen6 only needs render pipe_control now */
+	if (IS_GEN6(dev))
+		render_mask = GT_PIPE_NOTIFY;
+
 	dev_priv->gt_irq_mask_reg = ~render_mask;
 	dev_priv->gt_irq_enable_reg = render_mask;
 
 	I915_WRITE(GTIIR, I915_READ(GTIIR));
 	I915_WRITE(GTIMR, dev_priv->gt_irq_mask_reg);
+	if (IS_GEN6(dev))
+		I915_WRITE(GEN6_RENDER_IMR, ~GEN6_RENDER_PIPE_CONTROL_NOTIFY_INTERRUPT);
 	I915_WRITE(GTIER, dev_priv->gt_irq_enable_reg);
 	(void) I915_READ(GTIER);