Steam Controller

The Steam Controller is a game controller developed by Valve, which features two trackpads (in place of thumbsticks) with haptic feedback, and sixteen buttons. The Steam controller is designed not only for games supporting traditional controllers, but also for games that support keyboard and mouse.

Kernel
The Steam Controller is fully supported by Linux without the need for a specific device driver, however it does require USB and user level driver support.

Permissions
If Steam was installed manually or from an overlay, and ConsoleKit or systemd is not being used, create the following udev rules file:

The above udev rule will only grant access to the Steam Controller for users in the group:

If Steam was installed manually and ConsoleKit or systemd is being used, create the following udev rules file:

The above udev rule will automatically grant access (via ACLs) to the Steam Controller for logged in users.

If Steam was installed from anyc's Steam overlay, a udev rules file that supports ConsoleKit and systemd should already be installed with the ebuild.

Next, reload the udev rules files and trigger a device event for the new rule:

Once the udev rules files are reloaded, the user using the Steam Controller will need to log out/in for the correct permissions to be applied.