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hwmon: (it87) Add support for old automatic fan speed control

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Add support for the automatic fan speed control interface as
implemented by IT8705F chips up to revision F and IT8712F chips up to
revision G. This implementation fits very well in our standard sysfs
interface.

I implemented the old and not the new interface because the only chip
I have at hand is an old one, and the new interface is more difficult
to map to the standard sysfs interface. Adding support later should be
possible though, if someone with a supported chip is interested.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
This commit is contained in:
Jean Delvare
2010-03-05 22:17:21 +01:00
parent 404a552d8a
commit 4f3f51bc21
2 changed files with 205 additions and 4 deletions
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27
Documentation/hwmon/it87
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@@ -146,11 +146,34 @@ Fan speed control
-----------------
The fan speed control features are limited to manual PWM mode. Automatic
"Smart Guardian" mode control handling is not implemented. However
if you want to go for "manual mode" just write 1 to pwmN_enable.
"Smart Guardian" mode control handling is only implemented for older chips
(see below.) However if you want to go for "manual mode" just write 1 to
pwmN_enable.
If you are only able to control the fan speed with very small PWM values,
try lowering the PWM base frequency (pwm1_freq). Depending on the fan,
it may give you a somewhat greater control range. The same frequency is
used to drive all fan outputs, which is why pwm2_freq and pwm3_freq are
read-only.
Automatic fan speed control (old interface)
-------------------------------------------
The driver supports the old interface to automatic fan speed control
which is implemented by IT8705F chips up to revision F and IT8712F
chips up to revision G.
This interface implements 4 temperature vs. PWM output trip points.
The PWM output of trip point 4 is always the maximum value (fan running
at full speed) while the PWM output of the other 3 trip points can be
freely chosen. The temperature of all 4 trip points can be freely chosen.
Additionally, trip point 1 has an hysteresis temperature attached, to
prevent fast switching between fan on and off.
The chip automatically computes the PWM output value based on the input
temperature, based on this simple rule: if the temperature value is
between trip point N and trip point N+1 then the PWM output value is
the one of trip point N. The automatic control mode is less flexible
than the manual control mode, but it reacts faster, is more robust and
doesn't use CPU cycles.