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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: Jean Delvare <khali@linux-fr.org>
hifive-unleashed-5.1
Jean Delvare 2006-12-12 18:18:27 +01:00 committed by Jean Delvare
parent 315c7113b5
commit e9cea64601
1 changed files with 38 additions and 4 deletions
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@ -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.