So, my KVM switch breaks the pmsi driver in an interesting way.  If I switch
away and back, the KVM starts using the standard 3-byte protocol again.
Windows is apparently aware of the switch, enough to resend the "change
protocols" message.

I was thinking about this, and it seems that it would be useful for the driver
to know about protocol changes.

I was also thinking about my 5-button mouse.

It seems to me that a single PS/2 mouse driver that could re-negotiate
protocols under some circumstances might be a very useful thing to have.

With KVM switches, it's comprehensible to imagine a system *changing* from a
3-button mouse to a 5-button mouse with scrollwheel, while up and running.
Currently, we have no way to support this; if the pmsi driver doesn't probe
a mouse, it never gets used, and if we *do* configure pmsi, we can never
use a mouse that uses the 3-byte protocol.

The major thing missing is any idea of what happens to tell Windows that
it's time to re-enable the advanced protocol.  Apart from that, everything
should be easy enough to do.

So... Would there be interest in a revised psm.c that supports multiple
protocols, and can change protocols dynamically under some circumstances?

-s