Kernel driver w83791d

Supported chips:

Author: Charles Spirakis <>

This driver was derived from the w83781d.c and w83792d.c source files.




Additional contributors:

Module Parameters

  • init boolean

    (default 0)

    Use ‘init=1’ to have the driver do extra software initializations. The default behavior is to do the minimum initialization possible and depend on the BIOS to properly setup the chip. If you know you have a w83791d and you’re having problems, try init=1 before trying reset=1.

  • reset boolean

    (default 0)

    Use ‘reset=1’ to reset the chip (via index 0x40, bit 7). The default behavior is no chip reset to preserve BIOS settings.

  • force_subclients=bus,caddr,saddr,saddr

    This is used to force the i2c addresses for subclients of a certain chip. Example usage is force_subclients=0,0x2f,0x4a,0x4b to force the subclients of chip 0x2f on bus 0 to i2c addresses 0x4a and 0x4b.


This driver implements support for the Winbond W83791D chip. The W83791G chip appears to be the same as the W83791D but is lead free.

Detection of the chip can sometimes be foiled because it can be in an internal state that allows no clean access (Bank with ID register is not currently selected). If you know the address of the chip, use a ‘force’ parameter; this will put it into a more well-behaved state first.

The driver implements three temperature sensors, ten voltage sensors, five fan rotation speed sensors and manual PWM control of each fan.

Temperatures are measured in degrees Celsius and measurement resolution is 1 degC for temp1 and 0.5 degC for temp2 and temp3. An alarm is triggered when the temperature gets higher than the Overtemperature Shutdown value; it stays on until the temperature falls below the Hysteresis value.

Voltage sensors (also known as IN sensors) report their values in millivolts. An alarm is triggered if the voltage has crossed a programmable minimum or maximum limit.

Fan rotation speeds are reported in RPM (rotations per minute). An alarm is triggered if the rotation speed has dropped below a programmable limit. Fan readings can be divided by a programmable divider (1, 2, 4, 8, 16, 32, 64 or 128 for all fans) to give the readings more range or accuracy.

Each fan controlled is controlled by PWM. The PWM duty cycle can be read and set for each fan separately. Valid values range from 0 (stop) to 255 (full). PWM 1-3 support Thermal Cruise mode, in which the PWMs are automatically regulated to keep respectively temp 1-3 at a certain target temperature. See below for the description of the sysfs-interface.

The w83791d has a global bit used to enable beeping from the speaker when an alarm is triggered as well as a bitmask to enable or disable the beep for specific alarms. You need both the global beep enable bit and the corresponding beep bit to be on for a triggered alarm to sound a beep.

The sysfs interface to the global enable is via the sysfs beep_enable file. This file is used for both legacy and new code.

The sysfs interface to the beep bitmask has migrated from the original legacy method of a single sysfs beep_mask file to a newer method using multiple *_beep files as described in Documentation/hwmon/sysfs-interface.rst.

A similar change has occurred for the bitmap corresponding to the alarms. The original legacy method used a single sysfs alarms file containing a bitmap of triggered alarms. The newer method uses multiple sysfs *_alarm files (again following the pattern described in sysfs-interface).

Since both methods read and write the underlying hardware, they can be used interchangeably and changes in one will automatically be reflected by the other. If you use the legacy bitmask method, your user-space code is responsible for handling the fact that the alarms and beep_mask bitmaps are not the same (see the table below).

NOTE: All new code should be written to use the newer sysfs-interface specification as that avoids bitmap problems and is the preferred interface going forward.

The driver reads the hardware chip values at most once every three seconds. User mode code requesting values more often will receive cached values.

/sys files

The sysfs-interface is documented in the ‘sysfs-interface’ file. Only chip-specific options are documented here.


this file controls mode of fan/temperature control for fan 1-3. Fan/PWM 4-5 only support manual mode.

  • 1 Manual mode
  • 2 Thermal Cruise mode
  • 3 Fan Speed Cruise mode (no further support)
temp[1-3]_target defines the target temperature for Thermal Cruise mode. Unit: millidegree Celsius RW
temp[1-3]_tolerance temperature tolerance for Thermal Cruise mode. Specifies an interval around the target temperature in which the fan speed is not changed. Unit: millidegree Celsius RW

Alarms bitmap vs. beep_mask bitmask

For legacy code using the alarms and beep_mask files:

Signal Alarms beep_mask Obs
in0 (VCORE) 0x000001 0x000001  
in1 (VINR0) 0x000002 0x002000 <== mismatch
in2 (+3.3VIN) 0x000004 0x000004  
in3 (5VDD) 0x000008 0x000008  
in4 (+12VIN) 0x000100 0x000100  
in5 (-12VIN) 0x000200 0x000200  
in6 (-5VIN) 0x000400 0x000400  
in7 (VSB) 0x080000 0x010000 <== mismatch
in8 (VBAT) 0x100000 0x020000 <== mismatch
in9 (VINR1) 0x004000 0x004000  
temp1 0x000010 0x000010  
temp2 0x000020 0x000020  
temp3 0x002000 0x000002 <== mismatch
fan1 0x000040 0x000040  
fan2 0x000080 0x000080  
fan3 0x000800 0x000800  
fan4 0x200000 0x200000  
fan5 0x400000 0x400000  
tart1 0x010000 0x040000 <== mismatch
tart2 0x020000 0x080000 <== mismatch
tart3 0x040000 0x100000 <== mismatch
case_open 0x001000 0x001000  
0x800000 (modified via beep_enable)