• J.R. Oldroyd's avatar
    e1000: Try auto-negotiation for fixed 100 or 10 configuration · 9ab4dfce
    J.R. Oldroyd authored
    Currently if an e1000 interface is set to a fixed media configuration,
    for gigabit, it will participate in auto-negotiation as required by
    IEEE 802.3-2018 Clause 37. However, if set to fixed media configuration
    for 100 or 10, it does NOT participate in auto-negotiation.
    
    By my reading of Clauses 28 and 37, while auto-negotiation is optional
    for 100 and 10, it is not prohibited and is, in fact, "highly
    recommended".
    
    This patch enables auto-negotiation for fixed 100 and 10 media
    configuration, in a similar manner to that already performed for 1000.
    I.e., the patch enables advertising of just the manually configured
    settings with the goal of allowing the remote end to match the manually
    configured settings if it has them available.
    
    To be clear, this patch does NOT allow an em(4) interface that has been
    manually configured with specific media settings to respond to
    auto-negotiation by then configuring different parameters to those that
    were manually configured. The intent of this patch is to fully comply
    with the requirements of Clause 37, but for 100 and 10.
    
    The need for this has arisen on an em(4) link where the other end is
    under a different administrative control and is set to full
    auto-negotiation. Due to the cable length GigE is not working well. It
    is desired to set the em(4) end to "media 100baseTX mediatype
    full-duplex" which does work when both ends are configured that way.
    Currently, because em(4) does not participate in autoneg for this
    setting, the remote defaults to half-duplex - i.e., there's a duplex
    mismatch and things don't work. With this patch, em(4) would inform the
    remote that it has only 100baseTX full, the remote would match that and
    it will work.
    
    Approved by:	erj
    MFC after:	2 weeks
    Differential Revision:	https://reviews.freebsd.org/D34449
    9ab4dfce