What driver would the Steam Controller come with if not xinput?

I know this was talked about a while ago, that the Steam controller wouldn't work like a "regular controller" without Steam. So I'm curious what drivers are there if not xinput or dinput, both of which require MS licenses from what I've heard (please cmiiw), in which case it makes sense for Valve to not want to include that in their controller.

I guess this is more so a question for regular Linux junkies: what other drivers are available for Valve to adopt that would allow it to work not just on Linux but also macOS and Windows? Not that I use any of these systems, but just speaking from statistics, cause most buyers are going to be from Windows I reckon.

For Linux, does the Joystick API even support the back paddles? Gyro is likely unsupported from a quick search.