netdev - Re: Configuring synchronous ethernet with ethtool?

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Date:	Sat, 04 Apr 2015 14:59:10 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Richard Cochran <richardcochran@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Configuring synchronous ethernet with ethtool?

On Tue, 2015-03-17 at 17:11 +0100, Richard Cochran wrote:
> Dear list,
> 
> I need to configure Synchronous Ethernet (SyncE) on a per-port basis
> for a current project.  So, I have been thinking about how best to
> implement SyncE.  My first idea is to make this into a new ethtool
> operation, but I would like to get some feedback about the direction.
[...]
> So, my current idea is to have an ethtool option to set the SyncE mode
> to one of:
> 
> - master (1000 Mbit only)
> - slave
> - none
> 
> I am not sure whether the manual/preferred thing makes any sense.
> Maybe someone has insight into this?

The 'manual' setting matches terminology in IEEE 802.3 (section 40.5.2).
There's no mention of 'preferred' there but perhaps this switch will
claim to be a single-port if you say it should prefer slave mode.

As you know, 1000BASE-T also uses synchronous TX clocks; so does
10GBASE-T.  It might be useful to be able to set the flag for multiport
device on Linux systems with multiple ports connected by a software
bridge.  Both this and the manual settings could be useful for link
compatibility testing.

So, I like the idea but it should not be tied to SyncE only.

Ben.

-- 
Ben Hutchings
The most exhausting thing in life is being insincere. - Anne Morrow Lindberg

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