drm/i915: Warn when execlists changes context without IRQs

If an batch ends while the IRQs are not turned on the notification can
go missing and the GPU can hang. So generate a warning in this case.
Signed-off-by: Peter Antoine <peter.antoine@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_lrc.c

@@ -394,6 +394,12 @@ static void execlists_context_unqueue(struct intel_engine_cs *ring)
 
 	assert_spin_locked(&ring->execlist_lock);
 
+	/*
+	 * If irqs are not active generate a warning as batches that finish
+	 * without the irqs may get lost and a GPU Hang may occur.
+	 */
+	WARN_ON(!intel_irqs_enabled(ring->dev->dev_private));
+
 	if (list_empty(&ring->execlist_queue))
 		return;