Kernel driver max31785

Supported chips:

Author: Andrew Jeffery <>


The Maxim MAX31785 is a PMBus device providing closed-loop, multi-channel fan management with temperature and remote voltage sensing. Various fan control features are provided, including PWM frequency control, temperature hysteresis, dual tachometer measurements, and fan health monitoring.

For dual-rotor configurations the MAX31785A exposes the second rotor tachometer readings in attributes fan[5-8]_input. By contrast the MAX31785 only exposes the slowest rotor measurement, and does so in the fan[1-4]_input attributes.

Usage Notes

This driver does not probe for PMBus devices. You will have to instantiate devices explicitly.

Sysfs attributes

fan[1-4]_alarm Fan alarm.
fan[1-4]_fault Fan fault.
fan[1-8]_input Fan RPM. On the MAX31785A, inputs 5-8 correspond to the second rotor of fans 1-4
fan[1-4]_target Fan input target
in[1-6]_crit Critical maximum output voltage
in[1-6]_crit_alarm Output voltage critical high alarm
in[1-6]_input Measured output voltage
in[1-6]_label “vout[18-23]”
in[1-6]_lcrit Critical minimum output voltage
in[1-6]_lcrit_alarm Output voltage critical low alarm
in[1-6]_max Maximum output voltage
in[1-6]_max_alarm Output voltage high alarm
in[1-6]_min Minimum output voltage
in[1-6]_min_alarm Output voltage low alarm
pwm[1-4] Fan target duty cycle (0..255)
pwm[1-4]_enable 0: Full-speed 1: Manual PWM control 2: Automatic PWM (tach-feedback RPM fan-control) 3: Automatic closed-loop (temp-feedback fan-control)
temp[1-11]_crit Critical high temperature
temp[1-11]_crit_alarm Chip temperature critical high alarm
temp[1-11]_input Measured temperature
temp[1-11]_max Maximum temperature
temp[1-11]_max_alarm Chip temperature high alarm