On Tue, 26 Oct 1999 15:15:24 +0200 
 Matthias Drochner <drochner@zel459.zel.kfa-juelich.de> wrote:

 > What happens if I force my card to eg 100 half duplex? Then the
 > switch can't detect a link failure and has no reason to restart
 > nway. I'd say our driver has to initiate an autonegotiation session,
 > advertising only the bit(s) wanted by the user, if the media setting
 > is changed.

PHYs are supposed to do this when you program the ANAR register (this == send
an NWay code word).  Often, when you set the "autonegotiate enable" bit in
a PHY, it will perform NWay itself (and possibly self-program).

When you set e.g. 10baseT, the ANAR is programmed with "adv. 10baseT" only.

        -- Jason R. Thorpe <thorpej@nas.nasa.gov>