The latest BIOS updates (version 1.4.0 and above) to the Dell XPS 15 9575 2-in-1 have become a cause for concern as they seem to render the keyboard and touchpad unresponsive whenever a user tries to login to the Linux desktop environment. Those who have filed this bug have confirmed that this is indeed a BIOS issue as the problem was resolved upon downgrading to the older 1.2.0 BIOS version.
https://www.notebookcheck.net/Latest-Dell-XPS-15-9575-BIOS-updates-result-in-unresponsive-input-devices-when-logging-in-to-Linux.419972.0.html