of_get_required_opp_performance_state
EXPORT_SYMBOL_GPL(of_get_required_opp_performance_state);
pstate = of_get_required_opp_performance_state(dev->of_node, index);
drvdata->performance_state = of_get_required_opp_performance_state(dev->of_node, 0);
int of_get_required_opp_performance_state(struct device_node *np, int index);