PM / Domains: Ensure subdomain is not in use before removing

The function pm_genpd_remove_subdomain() removes a subdomain from a
generic PM domain, however, it does not check if the subdomain has any
slave domains or device attached before doing so. Therefore, add a test
to verify that the subdomain does not have any slave domains associated
or any device attached before removing.

Signed-off-by: Jon Hunter <[e-mail]>
Acked-by: Kevin Hilman <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/base/power/domain.c

···
 
 	mutex_lock(&genpd->lock);
 
+	if (!list_empty(&subdomain->slave_links) || subdomain->device_count) {
+		pr_warn("%s: unable to remove subdomain %s\n", genpd->name,
+			subdomain->name);
+		ret = -EBUSY;
+		goto out;
+	}
+
 	list_for_each_entry(link, &genpd->master_links, master_node) {
 		if (link->slave != subdomain)
 			continue;
···
 		break;
 	}
 
+out:
 	mutex_unlock(&genpd->lock);
 
 	return ret;