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Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/hwmon/it87 | 27 |
1 files changed, 25 insertions, 2 deletions
diff --git a/Documentation/hwmon/it87 b/Documentation/hwmon/it87 index a96a70fe802..0083bd31735 100644 --- a/Documentation/hwmon/it87 +++ b/Documentation/hwmon/it87 @@ -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. |