Understanding and working with I2C driver with sysfs interface

amg88xx-kernel-driver-notes

0x68 device address is defined in the device tree: https://github.com/vuorioi/amg88xx-kernel-driver/blob/master/amg88xx-overlay.dts

dmesg output when not present:
# [   66.832427] amg88xx: probe of 1-0068 failed with error -121

Therefore, without the device connected, the sysfs paths are not loaded

other-references

Kernel docs:
* https://www.kernel.org/doc/html/latest/i2c/writing-clients.html

e.g. note: this explains how "i2c_rdwr_ioctl_data" can be used for combined read/write transaction without stop in between


Other kernel module projects:
* https://github.com/akoskovacs/kmod_example
* https://github.com/tejasatgithub/Linux-i2c-client-driver
* https://github.com/greendrm/pb206x-i2c
* https://github.com/vpcola/chip_i2c

terminal-steps.sh

# Install kernel headers
sudo apt-get install -y raspberrypi-kernel-headers
# Upgrade system (install latest kernel, etc.)
sudo apt upgrade -y

# Reboot

git clone https://github.com/vuorioi/amg88xx-kernel-driver
cd amg88xx-kernel-driver

# Create device tree overlay and load
dtc -W no-unit_address_vs_reg -O dtb -I dts -o amg88xx.dtbo amg88xx-overlay.dts
sudo dtoverlay amg88xx.dtbo

# Build kernel module and load
make
sudo insmod amg88xx.ko

# Initialise
sysfs_root="/sys/bus/i2c/devices/$(grep "amg88xx$" /sys/bus/i2c/devices/*/name | cut -d'/' -f6)"
sudo sh -c "echo normal > ${sysfs_root}/device_mode"