Mouse swapping on a laptop

[Bill Freeman]

Derek Martin writes:
 > While again, I didn't spend much time on it, the problem with using a
 > PS/2 mouse seems to be that Linux sees that and the internal mouse
 > device as the same logical device (/dev/psaux), with the same
 > configuration.  However, obviously that's not true in reality.  I know
 > of no way to handle two different configurations on the same device...

	I suspect that this is actually a BIOS issue.  Probably the
same hardware is used to interface the internal mouse and the PS/2
socket, with a wee bit of steering logic.  If I'm correct, at boot
time the BIOS "probes" for a mouse with the steering set for the
external connector, and if it finds none, flips the "switch", and
initializes the internal mouse.  So either mouse gets talked to by the
Linux kernel via the same hardware register set, and /dev/psaux is,
in fact, totally correct for both.

	If the switching control bit is readable, you could
conceivably as a module to read it, and adjust the mouse configuration
accordingly.  That would be chip set, and maybe even brand/model
specific, however.  Another hope would be for the BIOS to provide a
callback interface to query the mouse choice.

							Bill