drm/i915: Check the execlist queue for pending requests before declaring idle

Including a check against the execlist queue before calling the engine
idle and passing hangcheck.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170721123238.16428-6-chris@chris-wilson.co.ukSigned-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_engine_cs.c

@@ -1283,6 +1283,10 @@ bool intel_engine_is_idle(struct intel_engine_cs *engine)
 	if (port_request(&engine->execlist_port[0]))
 		return false;
 
+	/* ELSP is empty, but there are ready requests? */
+	if (READ_ONCE(engine->execlist_first))
+		return false;
+
 	/* Ring stopped? */
 	if (!ring_is_idle(engine))
 		return false;