All Focusrite USB audio interfaces are class compliant meaning that they work “out of the box” on Linux as audio and MIDI interfaces (although on Gen 3/4/Vocaster you need to disable MSD mode first ...
The FCP driver itself supports all Focusrite USB audio interfaces since the 2nd Gen Scarletts, so support for the other devices will be added here later. Until then, the Linux Scarlett2 driver ...