Thanks to the wiki troubleshooting guide, Borderlands 2 under Steam now works OK with a keyboard and mouse, but it's horrid in my cramped work area. So I bought a game controller (Gamesir T4N) which works in USB connection - after a few kernel tweaks, jstest shows all the buttons and joysticks working correctly.
In Steam, I've configured Borderlands to us steam's controller mapping, and AFAICT the buttons work in the configurator. But when I play the game, no sign of controller support, and I'm back to the keyboard
Reading the wiki, I may have some misconfiguration: I think from earlier times, my /etc/portage/package.accept_keywords selects a few items from the steam-overlay, rather than everything. Dunno if that's relevant.

