Re: disabling mediaopts for if_wm(4)

[Thor Lancelot Simon <tls%panix.com@localhost>]

On Wed, May 10, 2017 at 09:35:44AM +0800, Paul Goyette wrote:
> 
> So, what is the magic incantation to set the interface to 100TX FDX, but
> with flow/pause disabled?

You can't.  Or, more rightly, you can't do it the way you probably want to.

If you explicitly set a speed and duplex, you will disable autonegotiation,
because we do not separately control autonegotiation.  So you can force the
use of 100baseTX/FDX, but we will then not do nway, parallel autodetection
may fail to correctly guess the link duplex, and if you can't hardwire the
link partner you are likely to end up with a duplex mismatch and terrible
performance.

Indeed it's possible that if you've actually already explicitly set the speed
and duplex, what you're actually seeing is the consequence not of flow control
but of a duplex mismatch.

What we should probably do is what most other OSes do: if the user explicltly
sets a speed/duplex or other media options, perform autonegotiation but
restrict the modes we are willing to negotiate to only what the user chose.

Expressly disabling autonegotation should require another deliberate choice
by the user -- or just be impossible, as it has been on e.g. OS X for years.

But we can't do that now.  It'd be lovely if someone cared to make it so we
could.

Thor