ssize_t state_show (struct device * dev, struct device_attribute * attr, char * buf);
show returns the current power state of the device. '0' indicates the device is on. Other values (1-3) indicate the device is in a low power state.
store sets the current power state, which is an integer value between 0-3. If the device is on ('0'), and the value written is greater than 0, then the device is placed directly into the low-power state (via its driver's ->suspend method). If the device is currently in a low-power state, and the value is 0, the device is powered back on (via the ->resume method). If the device is in a low-power state, and a different low-power state is requested, the device is first resumed, then suspended into the new low-power state.