drm/i915: Suppress busy status for engines if wedged

If the driver is wedged, HW state may be very inconsistent and
report that it is still busy, even though we have stopped using it. This
can lead to a double *ERROR* rather than a graceful cleanup after
wedging.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170330145041.9005-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem.c

@@ -3112,9 +3112,7 @@ i915_gem_idle_work_handler(struct work_struct *work)
 	 * Wait for last execlists context complete, but bail out in case a
 	 * new request is submitted.
 	 */
-	wait_for(READ_ONCE(dev_priv->gt.active_requests) ||
-		 intel_engines_are_idle(dev_priv),
-		 10);
+	wait_for(intel_engines_are_idle(dev_priv), 10);
 	if (READ_ONCE(dev_priv->gt.active_requests))
 		return;
 

drivers/gpu/drm/i915/intel_engine_cs.c

@@ -1111,6 +1111,15 @@ bool intel_engines_are_idle(struct drm_i915_private *dev_priv)
 	struct intel_engine_cs *engine;
 	enum intel_engine_id id;
 
+	if (READ_ONCE(dev_priv->gt.active_requests))
+		return false;
+
+	/* If the driver is wedged, HW state may be very inconsistent and
+	 * report that it is still busy, even though we have stopped using it.
+	 */
+	if (i915_terminally_wedged(&dev_priv->gpu_error))
+		return true;
+
 	for_each_engine(engine, dev_priv, id) {
 		if (!intel_engine_is_idle(engine))
 			return false;