HP Fan reporting and control driver

A kernel platform driver to display and control fan speeds on a range of HP ProBook/EliteBook laptops, using ACPI methods.

Fair warning!

This module is currently a proof-of-concept and not for casual use!

In particular, fan control is not yet implemented, fan speed reporting is flaky and there are no checks or safeguards.

Embedded Controller hangs and other gremlins are to be expected.

As of yet, do not use if you don't know what you are doing!

Installing

Clone this repo

git clone https://github.com/cristianchelu/hp_acpi_fan.git

Build

cd hp_acpi_fan
make

and load the module

sudo insmod hp_acpi_fan.ko

Parameters

This module takes two optional parameters, representing the ACPI methods to use when reading/writing fan speed values. If not set, it will try to auto-detect available methods.

readtype={none,gtmm,gfve,gfrm,kgfs,gfsd,i2cc}

ctrltype={auto,stmm,ksfs,kfcl,sfsd,i2cc}

Testing

You may see the control methods available in your BIOS by disassembling your DSDT table, and then poking around the relevant methods using acpi_call

Extracting the DSDT

First extract the compiled contents

cat /sys/firmware/acpi/tables/DSDT > dsdt.dat

then disassemble

iasl -d dsdt.dat

You should then have the decompiled dsdt.dsl file in the current directory.

More information available here: https://wiki.archlinux.org/index.php/DSDT

Poking around

• Note! BEFORE poking around, make sure to search how to reset the EC of your laptop model, be it by removing the battery or some key combination. Writing unexpected data to the EC or other controllers can cause system instability!

Install the acpi_call module by following the instructions here: https://github.com/nix-community/acpi_call

Search the dsdt.dsl file for methods relating to fan control and reporting. (eg. methods writing to registries named CFAN or PWM0 may be related to fan control).

Use acpi_call to probe said functions and compare their output with expected results. For example, running the following as root

echo "\_SB.PCI0.LPCB.EC0.GFSD" > /proc/acpi/call && cat /proc/acpi/call

should return fan speed as a percentage, if such method exists.

likewise,

echo "\_SB.PCI0.LPCB.EC0.SFSD 50" > /proc/acpi/call && cat /proc/acpi/call

should set fan speed to 50%.

Use your deduction skills and exercise caution.

ACPI methods

The following methods relating to fan reporting and control were found by disassembling the DSDT tables of an Elitebook 8440p, 8450w, 8460p and x360 1020 G2. They may, however, work on other model-ranges as well, as reported here.

Not all methods work on all laptops.

Reporting methods

\_TZ methods

On the Elitebook x360 1020 G2, but not on the older models, the following methods are present in the thermal zone region:

• GTMM - Debug string expands it to GetThermalStatus

  Not completely analyzed yet.

• GFVE - GetFanValueExtended?

  Takes one argument in the form 1|2 and returns either FRDC or FR2C raw value (either Fan0 or Fan1 tachometer value).

• GTFV - GetTargetFanValue?

  Takes one argument in the form 1|2 and returns either FTGC or FT2C raw value (either Fan0 or Fan1 target speed value).

• GFRM - GetFanRPM

  Takes no arguments. Reads FRDC (Fan0 value) and returns it as an RPM value.

\_SB.PCI0.LPCB.EC methods

• GFSD - GetFanSpeed(D?)

  Takes no arguments, reads the PWM0 register and returns its value normalized to 0-100.

  Note On the 8440p the fan is controlled by a separate IC, and the PWM value is returned from there.

• KGFS - (K?)GetFanSpeed

  Takes no arguments, reads the CFAN register and returns it. Returns 0x14 if the EC is not available

• KRFS - (K?)Get(Right?)FanSpeed

  Takes no arguments, reads the PFAN register and returns it. Returns 0x1E if the EC is not available.

  On the 8540w it is used in the \_SB.GRFS method. Possibly relevant on laptops equipped with two fans.

Control methods

\_TZ methods

On the Elitebook x360 1020 G2, but not on the older models, the following methods are present in the thermal zone region:

• STMM - SetThermalStatus.

  Takes one Buffer argument, is pluripotent. Not analyzed yet.

• CTCT - Utility method. Uses MRPM (MaxRPM) register to convert a [0-100] input into a sane value for FTGC (Fan0Target).

\_SB.PCI0.LPCB.EC methods

• KFCL - (K?)FanControl

  Takes two arguments. Arg0 is checked to be [0-100] and written to CFAN. Arg1 is not checked and written to MFAC.

• KSFS - (K?)SetFanSpeed

  Takes one argument, writes it to CFAN unchecked

• SFSD - Takes one argument in [0-100], writes to PWM0 register.

Registers

The following \_SB.PCI0.LPCB.EC registers are present on all analyzed DSDTs:

• MFAC - Minimum fan speed when on AC. Writing to this register seems to have an effect on all tested models.
• CFAN - Fan speed control (%?). KFCL expects it to be [0-100] but other methods do not check.
• PFAN - No method writes to this. Presumably secondary fan speed %.
• PWM0 - bit 1 is "fan-off". bit 8 is unknown, SFSD seems to preserve it. bits 2-7 represent fan drive, lower numbers are faster speeds.

The following were only found in the Elitebook 1020:

• FTGC - Fan0 value.
• FT2C - Fan1 value.
• FTGC - Fan0 target value.
• FT2C - Fan1 target value.
• MRPM - Maximum RPM, used by CTCT.

This list will be expanded as more methods are found and understood.

Contributions are welcome!

Note on the 8440p

The tested laptop has an independent SMSC EMC2113 fan control chip on the I2C bus at addresses 5C/5D, and the control method is peculiar.

The EC initalizes it with a temperature lookup table, but the provided 'temperature' actually represents the desired PWM value, even if the chip has a separate PWM input.

The I2C bus and chip are accessible from ACPI via the \_SB.PCI0.LPCB.SMAB R/W method.

Consulting the datasheet, it is possible to switch this chip to a different LUT or direct control register, completely bypassing the EC. This, however, is currently beyond the scope of this module.

TODO

• Improve documentation
• Automatic control method detection
• Reporting PWM vs RPM / Dynamically register HWMON attributes
• Refactor and make sense of the quantum-zoo of registers
• MAYBE: i2c fan chip detection and direct control