ifconfig media support

[Donald Becker]

Note: I've added this response to
  http://cesdis.gsfc.nasa.gov/linux/misc/faq.html#ifconfig
Comments and suggestions welcome.

On Wed, 30 Dec 1998, Rainer Clasen wrote:

> The tulip driver doesn't yet support "ifconfig media foo", does it? Is

The problem is that this concept isn't well defined.
The people that implemented this ill-advised option to 'ifconfig' only saw a
tiny part of the issue, and implemented a hack that solved only their
specific problem.


____A Simple Answer____

Yes, a user-level can set the 'dev->ifport' value for the interface
and the Tulip driver will honor the value set.   Note: the ifport value
should only before set before the interface is marked "up".  Changing the
value during device operation is undefined.

The issue that each driver (in some cases, each card type!) uses a "native"
index of which media types are available.  The mapping from index to media
type often comes from the implementation details.  In the Tulip driver it
comes from the Digital SROM specification, in the 3c59x driver it's defined
by a configuration register bitfield, etc.

____The Real Story____

Here is an example that shows why this is a complicated problem: say
"100baseTx" is specified.  Does that mean
   We advertise 100baseTx-HD (only) using NWay autonegotiation.
   We advertise 100baseTx-HD and 100baseTx-HD using NWay autonegotiation,
         and use the negotiated duplex.
   We disable autonegotiation and force 100baseTx-HD.

The Tulip chip (and several other chip types) also has the option of using
either SYM (symbol mode) or MII (media independent interface) PHYs.  In the
Tulip driver "100baseTx" might mean any of six different transceiver
configurations.  We also have 10baseT, 100baseT4, 10baseF, 100baseFx,
gigabit Ethernet, and various intermediate speeds (e.g. wireless).


Donald Becker					  becker@cesdis.gsfc.nasa.gov
USRA-CESDIS, Center of Excellence in Space Data and Information Sciences.
Code 930.5, Goddard Space Flight Center,  Greenbelt, MD.  20771
301-286-0882	     http://cesdis.gsfc.nasa.gov/people/becker/whoiam.html