PS/2 and USB keyboard at the same time, where to start

[Sebastian Yepes F. [ESN]]

> In message: <20040710212822.GX41460 at seven.alameda.net>
>             Ulf Zimmermann <ulf at Alameda.net> writes:
> : I want to try myself on kernel hacking again and a thing which peaked my
> : interest was some emails a few days ago about making the kernel use both
> : PS/2 and USB keyboards at the same time. My questions is can anyone point
> : me at the relevant pieces of the kernel I should study about trying myself
> : on this?
>
> There's already a keyboard mux in the kernel.  You'll just need to
> make it max many to 1.
>
> Warner

How is this setup, I don't see no MUX stuff on the files device.hints or kern
conf.

can you please explain your self, thanks