drm/i915: Report engines are idle if already parked

If we have parked, then we must have passed an idleness test and still
be idle. We chose not to use this shortcut in the past so that we could
use the idleness test at any time and inspect HW. However, some HW like
Sandybridge, doesn't like being woken up frivolously, so avoid doing so.

References: 0b702dca ("drm/i915: Avoid waking the engines just to check if they are idle")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190227214159.7946-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_engine_cs.c

@@ -1072,7 +1072,7 @@ bool intel_engine_is_idle(struct intel_engine_cs *engine)
 	return ring_is_idle(engine);
 }
 
-bool intel_engines_are_idle(struct drm_i915_private *dev_priv)
+bool intel_engines_are_idle(struct drm_i915_private *i915)
 {
 	struct intel_engine_cs *engine;
 	enum intel_engine_id id;
@@ -1081,10 +1081,14 @@ bool intel_engines_are_idle(struct drm_i915_private *dev_priv)
 	 * 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_reset_failed(dev_priv))
+	if (i915_reset_failed(i915))
 		return true;
 
-	for_each_engine(engine, dev_priv, id) {
+	/* Already parked (and passed an idleness test); must still be idle */
+	if (!READ_ONCE(i915->gt.awake))
+		return true;
+
+	for_each_engine(engine, i915, id) {
 		if (!intel_engine_is_idle(engine))
 			return false;
 	}