drm/i915: Silence debugging DRM_ERROR for failing to suspend vlv powerwells

If we try to suspend a wedged device following a GPU reset failure, we
will also fail to turn off the rc6 powerwells (on vlv), leading to a
*ERROR*. This is quite expected in this case, so the best we can do is
shake our heads and reduce the *ERROR* to a debug so CI stops
complaining.

Testcase: igt/gem_eio/in-flight-suspend #vlv
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105583
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180409094905.4516-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_drv.c

@@ -2468,10 +2468,13 @@ static void vlv_wait_for_gt_wells(struct drm_i915_private *dev_priv,
 	/*
 	 * RC6 transitioning can be delayed up to 2 msec (see
 	 * valleyview_enable_rps), use 3 msec for safety.
+	 *
+	 * This can fail to turn off the rc6 if the GPU is stuck after a failed
+	 * reset and we are trying to force the machine to sleep.
 	 */
 	if (vlv_wait_for_pw_status(dev_priv, mask, val))
-		DRM_ERROR("timeout waiting for GT wells to go %s\n",
-			  onoff(wait_for_on));
+		DRM_DEBUG_DRIVER("timeout waiting for GT wells to go %s\n",
+				 onoff(wait_for_on));
 }
 
 static void vlv_check_no_gt_access(struct drm_i915_private *dev_priv)