+
+
+Fan Control
+-----------
+
+Both PWM (pulse-width modulation) and DC fan speed control methods are
+supported. The right one to use depends on external circuitry on the
+motherboard, so the driver assumes that the BIOS set the method
+properly. The driver will report the method, but won't let you change
+it.
+
+When the PWM method is used, you can select the operating frequency,
+from 187.5 kHz (default) to 31 Hz. The best frequency depends on the
+fan model. As a rule of thumb, lower frequencies seem to give better
+control, but may generate annoying high-pitch noise. So a frequency just
+above the audible range, such as 25 kHz, may be a good choice; if this
+doesn't give you good linear control, try reducing it. Fintek recommends
+not going below 1 kHz, as the fan tachometers get confused by lower
+frequencies as well.
+
+When the DC method is used, Fintek recommends not going below 5 V, which
+corresponds to a pwm value of 106 for the driver. The driver doesn't
+enforce this limit though.
+
+Three different fan control modes are supported; the mode number is written
+to the pwm<n>_enable file.
+
+* 1: Manual mode
+ You ask for a specific PWM duty cycle or DC voltage by writing to the
+ pwm<n> file.
+
+* 2: Temperature mode
+ You define 3 temperature/fan speed trip points using the
+ pwm<n>_auto_point<m>_temp and _fan files. These define a staircase
+ relationship between temperature and fan speed with two additional points
+ interpolated between the values that you define. When the temperature
+ is below auto_point1_temp the fan is switched off.
+
+* 3: Fan speed mode
+ You ask for a specific fan speed by writing to the fan<n>_target file.
+
+Both of the automatic modes require that pwm1 corresponds to fan1, pwm2 to
+fan2 and pwm3 to fan3. Temperature mode also requires that temp1 corresponds
+to pwm1 and fan1, etc.