em(4) on FreeBSD is sometimes annoying

[sthaug at nethelp.no]

> Hasn't anyone really noticed yet that em(4) only appears when you boot
> FreeBSD with the interface physically attached to a switch for example?
> If you attach it later, after boot up, the interface won't power up and
> appear in the interface list (ifconfig)?

I'm afraid I don't see your problem at all. My em interfaces appear
as they should, even if not connected to a switch. And when I connect
an em interface to a switch, I get link and things work as expected.

> Steps to reproduce:
> 1) Switch your PC/laptop off. Really OFF, no reboot.
> 2) Disconnect the em(4) NIC from your switch.
> 3) Boot FreeBSD.
> 4) Plug in the ethernet cable.
> 5) Tataa! All leds at the NIC stay off. You won't be able to use em(4)
> unless you reboot your machine.
> 
> Something is not being initialized properly on em(4) devices, it seems. 

This may well be the case - but not that the em driver handles several
different chip models. You may have a problem which is specific to one
or a few chip models.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no