Nézd meg hogy milyen hwmonitor chiped van, és nézd meg a kernel dokumentációt IMHO
Szerk.: Idézet a 2.6.x kernel doksiból:
The LM85 has four fan speed monitoring modes. The ADM1027 has only two. Both have special circuitry to compensate for PWM interactions with the TACH signal from the fans. The ADM1027 can be configured to measure the speed of a two wire fan, but the input conditioning circuitry is different for 3-wire and 2-wire mode.