The PS/2 Keyboard accepts commands and sends responses to those commands, and also sends scan codes indicating when a key was pressed or released.
Ideally, each different type of PS/2 controller driver should provide some sort of standard/simple 'send byte/receive byte' interface, and the PS/2 Keyboard driver would use this interface without caring about lower level details (like what type of PS/2 controller the device is plugged into). The PS/2 Keyboard is a device that talks to a PS/2 controller using serial communication.
