cm4io-fan

kernel module and device tree overlay to add support for the EMC2301 fan controller on the Raspberry Pi Compute Module 4 IO Board.

Works with 5.10+ 64-bit kernels only.

Uses Traverse Technologies’ EMC2301 hwmon driver for their ten64 board, which you should definitely check out because it’s awesome.

Usage

Install dkms if you haven’t already:
```
sudo apt install dkms
```
Download the latest source .tar.gz from the releases page

Untar it to /usr/src/cm4io-fan-<version> and run the dkms install:

tar -xzvf 0.2.0.tar.gz -C /usr/src/
sudo dkms install cm4io-fan/0.2.0

Add these lines to your /boot/config.txt (adjust the rpm values for your specific fan, defaults are 3500 / 5500) and reboot.
See below for more config options.

# Enable I2C bus 1 on VideoCore (/dev/i2c-10 in Raspberry Pi OS)
dtparam=i2c_vc=on
# Enable CM4 IO Board fan controller
dtoverlay=cm4io-fan,minrpm=1000,maxrpm=5000

Some distributions may not automatically load the kernel module despite the devicetree entry; Raspberry Pi OS does, Ubuntu 21.10 does not, etc.
To make the module load, edit /etc/modules (or make a new file called /etc/modules-load.d/cm4io-fan.conf), adding this line:
```
emc2301
```

Install from git

Install dkms if you haven’t already:
```
sudo apt install dkms
```

Clone the repo

mkdir -p ~/src
cd ~/src
git clone https://github.com/neg2led/cm4io-fan.git
cd cm4io-fan

Run install.sh, feel free to inspect it yourself first. It will archive the current HEAD to /usr/src with an appropriate version, and run DKMS.

Config options

The device tree overlay has a few options, here’s the equivalent of a /boot/overlays/README info section:

Name:   cm4io-fan
Info:   Raspberry Pi Compute Module 4 IO Board fan controller
Load:   dtoverlay=cm4io-fan,<param>[=<val>]
Params: minrpm              RPM target for the fan when the SoC is below 
                            mintemp (default 3500)
        maxrpm              RPM target for the fan when the SoC is above
                            maxtemp (default 5500)
        midtemp             Temperature (in millicelcius) at which the fan
                            begins to speed up (default 50000)
        midtemp_hyst        Temperature delta (in millicelcius) below mintemp
                            at which the fan will drop to minrpm (default 2000)
        maxtemp             Temperature (in millicelcius) at which the fan 
                            will be held at maxrpm (default 70000)
        maxtemp_hyst        Temperature delta (in millicelcius) below maxtemp
                            at which the fan begins to slow down (default 2000)

many thanks to:

taudac/taudac-driver-dkms for helping me work out how the shit DKMS works
Traverse Technologies for the kernel module