[vortex] 3c590 media selection

[Donald Becker]

On Sun, 7 Jan 2001, Andrew Morton wrote:

> > IIRC, we must select the 10baseT transceiver for some significant time to
> > reliably detect 10baseT link beat, so we risk dropping a 10base2 packet if
> > we poll.
> 1.4 seconds.

Unrelated note: Autonegotation takes up to 3.0 seconds.  It used to be
documented as 2.4, but they missed an unlikely even-worse-case scenerio.

> In this case, dev->if_port is XCVR_10baseT, from `options'.  But there's
> no link beat, so `ok' remains at zero and we go on to select the next
> media type.
> 
> I tested 0.99Ra with the 3c590, BTW.  It too got stuck on the 10base2
> port when the 10baseT cable was removed.

> > > What happens is that the selection logic rotates to
> > > 10base2 and then gets stuck there because 10base2
> > > has no link beat indication.

Hmmm, after thinking about this for a while, it might make sense to have the
following semantics for the 3c590:
  if 10baseT link beat is ever detected, lock the media down to 10baseT.

It's pretty unlikely that a user would disconnect 10baseT and expect the
card to switch to 10base2.  The only case I can think of is using a 10base2
network as a fail-over when the 10baseT hub loses power.

It's much more likely that losing 10baseT link beat is temporary, and the
user doesn't expect the card to work until link beat returns.


Donald Becker				becker@scyld.com
Scyld Computing Corporation		http://www.scyld.com
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