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 <jonathanh@nvidia.com>
Acked-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/power/domain.c

@@ -1473,6 +1473,13 @@ int pm_genpd_remove_subdomain(struct generic_pm_domain *genpd,
 
 	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;
@@ -1491,6 +1498,7 @@ int pm_genpd_remove_subdomain(struct generic_pm_domain *genpd,
 		break;
 	}
 
+out:
 	mutex_unlock(&genpd->lock);
 
 	return ret;