drm/i915/guc: Don't take struct_mutex for object unreference

We no longer need to take the struct_mutex for freeing objects, and on
the finalisation paths here the mutex is not been used for serialisation
of the pointer access, so remove the BKL wart.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170214133420.7977-1-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/intel_guc_loader.c

@@ -714,12 +714,9 @@ fail:
 	DRM_DEBUG_DRIVER("uC fw fetch status FAIL; err %d, fw %p, obj %p\n",
 		err, fw, uc_fw->obj);
 
-	mutex_lock(&dev_priv->drm.struct_mutex);
-	obj = uc_fw->obj;
+	obj = fetch_and_zero(&uc_fw->obj);
 	if (obj)
 		i915_gem_object_put(obj);
-	uc_fw->obj = NULL;
-	mutex_unlock(&dev_priv->drm.struct_mutex);
 
 	release_firmware(fw);		/* OK even if fw is NULL */
 	uc_fw->fetch_status = INTEL_UC_FIRMWARE_FAIL;
@@ -793,16 +790,17 @@ void intel_guc_init(struct drm_i915_private *dev_priv)
 void intel_guc_fini(struct drm_i915_private *dev_priv)
 {
 	struct intel_uc_fw *guc_fw = &dev_priv->guc.fw;
+	struct drm_i915_gem_object *obj;
 
 	mutex_lock(&dev_priv->drm.struct_mutex);
 	guc_interrupts_release(dev_priv);
 	i915_guc_submission_disable(dev_priv);
 	i915_guc_submission_fini(dev_priv);
-
-	if (guc_fw->obj)
-		i915_gem_object_put(guc_fw->obj);
-	guc_fw->obj = NULL;
 	mutex_unlock(&dev_priv->drm.struct_mutex);
 
+	obj = fetch_and_zero(&guc_fw->obj);
+	if (obj)
+		i915_gem_object_put(obj);
+
 	guc_fw->fetch_status = INTEL_UC_FIRMWARE_NONE;
 }

drivers/gpu/drm/i915/intel_huc.c

@@ -274,12 +274,11 @@ fail:
 void intel_huc_fini(struct drm_i915_private *dev_priv)
 {
 	struct intel_uc_fw *huc_fw = &dev_priv->huc.fw;
+	struct drm_i915_gem_object *obj;
 
-	mutex_lock(&dev_priv->drm.struct_mutex);
-	if (huc_fw->obj)
-		i915_gem_object_put(huc_fw->obj);
-	huc_fw->obj = NULL;
-	mutex_unlock(&dev_priv->drm.struct_mutex);
+	obj = fetch_and_zero(&huc_fw->obj);
+	if (obj)
+		i915_gem_object_put(obj);
 
 	huc_fw->fetch_status = INTEL_UC_FIRMWARE_NONE;
 }