PM / runtime: Drop children check from __pm_runtime_set_status()

The check for "active" children in __pm_runtime_set_status(), when
trying to set the parent device status to "suspended", doesn't
really make sense, because in fact it is not invalid to set the
status of a device with runtime PM disabled to "suspended" in any
case. It is invalid to enable runtime PM for a device with its
status set to "suspended" while its child_count reference counter
is nonzero, but the check in __pm_runtime_set_status() doesn't
really cover that situation.

For this reason, drop the children check from __pm_runtime_set_status()
and add a check against child_count reference counters of "suspended"
devices to pm_runtime_enable().

Fixes: a8636c89648a (PM / Runtime: Don't allow to suspend a device with an active child)
Signed-off-by: Rafael J. Wysocki <[e-mail]>
Reviewed-by: Ulf Hansson <[e-mail]>
Reviewed-by: Johan Hovold <[e-mail]>

Documentation/power/runtime_pm.txt

···
       PM status to 'suspended' and update its parent's counter of 'active'
       children as appropriate (it is only valid to use this function if
       'power.runtime_error' is set or 'power.disable_depth' is greater than
-      zero); it will fail and return an error code if the device has a child
-      which is active and the 'power.ignore_children' flag is unset
+      zero)
 
   bool pm_runtime_active(struct device *dev);
     - return true if the device's runtime PM status is 'active' or its

drivers/base/power/runtime.c

···
 		goto out;
 	}
 
-	if (dev->power.runtime_status == status)
+	if (dev->power.runtime_status == status || !parent)
 		goto out_set;
 
 	if (status == RPM_SUSPENDED) {
-		/*
-		 * It is invalid to suspend a device with an active child,
-		 * unless it has been set to ignore its children.
-		 */
-		if (!dev->power.ignore_children &&
-			atomic_read(&dev->power.child_count)) {
-			dev_err(dev, "runtime PM trying to suspend device but active child\n");
-			error = -EBUSY;
-			goto out;
-		}
-
-		if (parent) {
-			atomic_add_unless(&parent->power.child_count, -1, 0);
-			notify_parent = !parent->power.ignore_children;
-		}
-		goto out_set;
-	}
-
-	if (parent) {
+		atomic_add_unless(&parent->power.child_count, -1, 0);
+		notify_parent = !parent->power.ignore_children;
+	} else {
 		spin_lock_nested(&parent->power.lock, SINGLE_DEPTH_NESTING);
 
 		/*
···
 		dev->power.disable_depth--;
 	else
 		dev_warn(dev, "Unbalanced %s!\n", __func__);
+
+	WARN(!dev->power.disable_depth &&
+	     dev->power.runtime_status == RPM_SUSPENDED &&
+	     !dev->power.ignore_children &&
+	     atomic_read(&dev->power.child_count) > 0,
+	     "Enabling runtime PM for inactive device (%s) with active children\n",
+	     dev_name(dev));
 
 	spin_unlock_irqrestore(&dev->power.lock, flags);
 }