Re: half-/full-duplex ethernet and ifconfig

[David Laight <david%l8s.co.uk@localhost>]

On Wed, Nov 14, 2012 at 11:57:11AM +0900, Masanobu SAITOH wrote:
> 
>  Currently, we have no API to specify an advertise setting for auto
> negotiation particularly. I think it's useful on some cases.

When I was playing with ethernet PHY/MAC setup many years ago I
basically decided that the best way to 'force' the mode was to
restrict the bits in the ANAR (AutoNegotiate Advertise Reg) rather
than forcing the MAC itself into a specific mode.
That way you are much less likely to get painful duplex mismatches.

The real PITA is that, while you can read the response register,
you can't easily find the actual operating mode (not without
reading implementation specific registers) because the PHY might
be connected to an old hub that only does 10/100 HDX and uses
autodetect (not autonegotiate).
Ifd you aren't very careful you can use the old settings and
get a HDX/FDX mismatch.
I guess this was much more likely 10 years ago, but 10/100 hubs
are still lurking in dev labs (and are often the only thing lurking
unused for a test LAN.

        David

-- 
David Laight: david%l8s.co.uk@localhost