Apple Studio Display Brightness Control

A small command line utility to get or set the brightness level for Apple Studio Displays from Linux.

Getting started

The software is written in Rust and uses libusb in the background. There are no binary releases, which means you will need to install Rust (or rewrite it in C). In either case you will need to install libusb with your distros package manager. So when Rust and libusb is setup::

git clone https://github.com/juliuszint/asdbctl.git && cd asdbctl
cargo build --release
sudo ./target/release/asdbctl get

The program will need root permissions to function properly.

Background

Dumping the USB traffic on macOS with Wireshark and setting the proper filters will show the USB Control transfers to set the brightness:

bmRequestType: 0x21
bRequest     : 0x9
wValue       : 0x0301
wIndex:      : 0x000c
wLength      : 0x7

with this data package when setting it to the minimum brightness value:

[ 0x01, 0x90, 0x01, 0x00, 0x00, 0x00, 0x00 ]

The 0x90 and 0x01 are the brightness value encoded with the least significant byte first (LSB).

Its possible to operate the Studio Display in 3 different USB configurations and Linux will use the first. This means that the USB interface number for controlling the brightness is not 0xc (extracted from the dump) but 0x7.

Related projects

Other projects that helped along the way were LG-ultrafine-brightness and acdcontrol.