CommentStreams:3955462abeb6787a0c8252871eca3b54

Found it. The problem is, the misusing of wire color. Typically a fan with pwm control has a blue wire. Geekworm controlled the fan by PWM, but has a yellow wire. The yellow wire is used for tachometer/RPM control. In my case, i connected the blue fan wire to the yellow geekworm connector and it works.