IIO

IIO stands for the Industrial I/O subsystem of the Linux Kernel. It generally provides an interface to sensors like Accelerometers and Light sensors.

NixOS

The services using the subsystem can be enabled using this configuration in configuration.nix:

{ config }:
{
  hardware.sensor.iio.enable = true;
}

This will enable iio-sensor-proxy.

To test, monitor-sensor can be used, it will print out the current values of the sensors as they change, periodically. In the event nothing is detected after enabling, rebooting may help.

Software notes

It is unverified, but GNOME should automatically make use of the data when enabled to handle the rotation and automatic brightness of the display.

Hardware notes

Accelerometers

Sometimes, the accelerometers in different devices will be oriented in a way that it specific to that hardware, this is not a problem, but it is an issue to be considered. The Accelerometer orientation section on the iio-sensor-proxy project page explains how to fix this properly for your device. The NixOS specific note is that instead of creating an hwdb file, you would add services.udev.extraHwdb to your configuration.nix file.

{ config }:
{
  services.udev.extraHwdb = ''
    sensor:modalias:acpi:INVN6500*:dmi:*svn*ASUSTeK*:*pn*TP300LA*
     ACCEL_MOUNT_MATRIX=0, 1, 0; 1, 0, 0; 0, 0, 1
  '';
}