The PowerClamp driver

I have a problem with seeing the effect of powerclamp. First, I enabled intel powerclamp driver in my menuconfig. Then, I built a new kernel 3.9.7. After rebooting, I can see the module as /sys/class/thermal/cooling_device13. When I grep it. It shows,

cur_state:-1
max_state:50
type:intel_powerclamp

The cur_state =-1, which means invalid state. Why is this invalid state?

Thanks.