Open source firmware for Canon cameras, such as the 6D.

Procedure

Download from - https://builds.magiclantern.fm/. Go to 6D - https://builds.magiclantern.fm/6D-116.html
Install procedure - https://wiki.magiclantern.fm/install
Drivers for Canon - https://www.canon.co.uk/support/consumer_products/products/cameras/digital_slr/eos_6d.html?type=software&language=&os=linux
Issues with above - default links to windows download - eos6d-v116-win.zip - does this work on Linux? Download link at https://builds.magiclantern.fm/6D-116.html
Note EOS Utility appears to exist for 6D for Linux (wireless file transfer) - https://www.canon.co.uk/support/consumer_products/products/cameras/digital_slr/eos_6d.html?type=software&language=&os=linux%20(64-bit)
But frikkin firmware appears to exist only for Windows and Mac versions - [1]
6D firmware on site is only mac and windows - [2]
- Old firmware - Windows only - https://www.canondriver.net/tag/eos-6d-firmware-version-1-1-6-windows/
It's also true that firmware is read by camera, so the windows version should work (be downloadable) on a Linux box. [3]

Magic Lantern