drm/i915: Check execlist/ring status during hangcheck

Before we declare an engine as idle, check if there are any pending
execlist context-switches and if the ring itself reports as idle.
Otherwise, we may be left in a situation where we miss a crucial
execlist event (or something more sinister) yet the requests complete.
Since the seqno write happens, we believe the engine to be truly idle.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: NMichel Thierry <michel.thierry@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170721123238.16428-5-chris@chris-wilson.co.ukSigned-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_hangcheck.c

@@ -324,7 +324,7 @@ hangcheck_get_action(struct intel_engine_cs *engine,
 	if (engine->hangcheck.seqno != hc->seqno)
 		return ENGINE_ACTIVE_SEQNO;
 
-	if (i915_seqno_passed(hc->seqno, intel_engine_last_submit(engine)))
+	if (intel_engine_is_idle(engine))
 		return ENGINE_IDLE;
 
 	return engine_stuck(engine, hc->acthd);