drm/i915: Always stop the rings before a missing GPU reset

Always try to stop the rings, even if the GPU reset itself has been
disabled (via modparam i915.reset). This should at least stop the hw
from spinning in the background consuming resources (e.g. power and
memory bandwidth) letting the system rest-in-peace.

References: https://bugs.freedesktop.org/show_bug.cgi?id=103260
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171013131218.18013-2-chris@chris-wilson.co.uk
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>

drivers/gpu/drm/i915/intel_uncore.c

@@ -1403,6 +1403,9 @@ static void i915_stop_engines(struct drm_i915_private *dev_priv,
 	struct intel_engine_cs *engine;
 	enum intel_engine_id id;
 
+	if (INTEL_GEN(dev_priv) < 3)
+		return;
+
 	for_each_engine_masked(engine, dev_priv, engine_mask, id)
 		gen3_stop_engine(engine);
 }
@@ -1742,16 +1745,12 @@ static reset_func intel_get_gpu_reset(struct drm_i915_private *dev_priv)
 
 int intel_gpu_reset(struct drm_i915_private *dev_priv, unsigned engine_mask)
 {
-	reset_func reset;
+	reset_func reset = intel_get_gpu_reset(dev_priv);
 	int retry;
 	int ret;
 
 	might_sleep();
 
-	reset = intel_get_gpu_reset(dev_priv);
-	if (reset == NULL)
-		return -ENODEV;
-
 	/* If the power well sleeps during the reset, the reset
 	 * request may be dropped and never completes (causing -EIO).
 	 */
@@ -1771,7 +1770,9 @@ int intel_gpu_reset(struct drm_i915_private *dev_priv, unsigned engine_mask)
 		 */
 		i915_stop_engines(dev_priv, engine_mask);
 
-		ret = reset(dev_priv, engine_mask);
+		ret = -ENODEV;
+		if (reset)
+			ret = reset(dev_priv, engine_mask);
 		if (ret != -ETIMEDOUT)
 			break;