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Commit e9cea646 authored by Jean Delvare's avatar Jean Delvare Committed by Jean Delvare
Browse files

hwmon/f71805f: Document the fan control features 



Document the different fan control methods, list their options, and give
some hints for best results.

Signed-off-by: default avatarJean Delvare <khali@linux-fr.org>
parent 315c7113

Documentation/hwmon/f71805f

+38 −4
Original line number Diff line number Diff line
@@ -13,8 +13,8 @@ Thanks to Denis Kieft from Barracuda Networks for the donation of a 
test system (custom Jetway K8M8MS motherboard, with CPU and RAM) and

for providing initial documentation.



Thanks to Kris Chen from Fintek for answering technical questions and

providing additional documentation.

Thanks to Kris Chen and Aaron Huang from Fintek for answering technical

questions and providing additional documentation.



Thanks to Chris Lin from Jetway for providing wiring schematics and

answering technical questions.
@@ -28,8 +28,7 @@ capabilities. It can monitor up to 9 voltages (counting its own power 
source), 3 fans and 3 temperature sensors.



This chip also has fan controlling features, using either DC or PWM, in

three different modes (one manual, two automatic). The driver doesn't

support these features yet.

three different modes (one manual, two automatic).



The driver assumes that no more than one chip is present, which seems

reasonable.
@@ -103,3 +102,38 @@ sensor. Each channel can be used for connecting either a thermal diode 
or a thermistor. The driver reports the currently selected mode, but

doesn't allow changing it. In theory, the BIOS should have configured

everything properly.





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. 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:



* Manual mode

  You ask for a specific PWM duty cycle or DC voltage.



* Fan speed mode

  You ask for a specific fan speed. This mode assumes that pwm1

  corresponds to fan1, pwm2 to fan2 and pwm3 to fan3.



* Temperature mode

  You define 3 temperature/fan speed trip points, and the fan speed is

  adjusted depending on the measured temperature, using interpolation.

  This mode is not yet supported by the driver.