Re: em(4) does not autonegotiate when fixed media is set

From: J.R. Oldroyd <>
Date: Wed, 02 Mar 2022 17:04:21 UTC
On Wed, 2 Mar 2022 17:21:22 +0100 Lutz Donnerhacke <> wrote:
> On Wed, Mar 02, 2022 at 04:40:38PM +0100, wrote:
> > Is that what is expected? When using the above command I would expect
> > that 100MBit/sec is used, not that the card negotiates with the peer
> > something else. But my expectations might be wrong...  
> Negotation of a given subset is useful. Some devices do not work without
> negotiation enabled, others refuse to work in this case. Standard requires
> autonegotiation for 1000TX, recommends it for lower speeds (otherwise assume
> half duplex). For 1000FX the situation is unclear, depends on the year the
> device was manufactured ... Today autoneg is expected on all interfaces even
> with a limited subset of capabilies.

The patch enables autonegotiation for just the configured setting, not full
autonegotiation.  The intent is to let the other end know that we only have
the one configured setting.

At present, the other end appears to be syncing to the 100baseTX speed but
it does indeed appear to be choosing half-duplex, so the link does not work
when the FreeBSD end has been configured for full-duplex.

The only thing I am not sure about is whether or not the wait_to_complete
parameter should be cleared in this case.  I suspect it should be.  There
is the case that the other end may not attempt any autonegotiation dialog
either, and we do not want to hang waiting for it.  I am not able to test
this situation, though.