So basically, when you use a Steam Controller, you can bind and remap buttons and inputs on the controller to keys or buttons on a normal gamepad (so you can customize any game controls). The problem comes in because under Solus, the Steam Controller will not emulate any gamepad inputs that you assign. This is an issue that has arisen on different distros in my time using Linux - seems like it's something to do with uinput rules?
Here's my notes:
Starting with terminal shows that Steam couldn’t open /dev/uinput for writing. The exact error is this bit:
Steam Controller reserving XInput slot 0 Couldn't initialize virtual gamepad: Couldn't open /dev/uinput for writing
With the full error being found here on pastebin.
In its starting state, the controller didn't run too stably, and would sometimes drop out when browsing the menus in Big Picture Mode.
Switching to Steam’s beta branch helped the controller to remain stable, but did nothing for joystick emulation.
Turning off Linux Steam Integration to use Valve’s Steam Client didn’t help – it just made the Steam Overlay not grab onto the game windows.
Restarting my computer didn't fix the issue either.
Note that I'm using Solus 1.2.1 64-bit, the latest Steam beta, and a wired Steam Controller, updated to the latest firmware. Games tested: Nuclear Throne, CrossCode, and Hyper Light Drifter