netdev - Re: [PATCH] phylib: fix forced mode misbehaviour for aneg off case

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Message-ID: <20080703191815.GG17872@solarflare.com>
Date:	Thu, 3 Jul 2008 20:18:17 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Anton Vorontsov <avorontsov@...mvista.com>
Cc:	Stephen Hemminger <shemminger@...tta.com>,
	Jeff Garzik <jgarzik@...ox.com>,
	Andy Fleming <afleming@...escale.com>, netdev@...r.kernel.org
Subject: Re: [PATCH] phylib: fix forced mode misbehaviour for aneg off case

Anton Vorontsov wrote:
> On Thu, Jul 03, 2008 at 10:41:43AM -0700, Stephen Hemminger wrote:
> > On Thu, 3 Jul 2008 21:16:14 +0400
> > Anton Vorontsov <avorontsov@...mvista.com> wrote:
> > 
> > > With disabled autonegotiation and link absence, phylib will place phy
> > > into the forcing mode, thus will start calling phy_force_reduction().
> > > That means that for the drivers that are using phylib we can't actually
> > > set fixed speed for the link.
> > > 
> > > For example:
> > > 
> > > # ethtool -s eth0 autoneg off speed 1000
> > 
> > FYI autonegotiation is required in gigabit mode per 802 spec.
 
This is technically correct, but all "negotiated" settings can be manually
configured such that only a single possible configuration is advertised
during auto-negotiation.

> Thanks for the information. FWIW, that behaviour observed for
> speed 100 or speed 10, too.
> 
> As for gbit, this is interesting indeed. If we're not permitted to
> disable aneg, how could we force the PHY to use gigabit, so that it
> will not try to downgrade? I mean ethtool option.

You should be able to use
"ethtool -s eth0 autoneg on speed 1000 duplex full" (you have to specify
all three).  Not all drivers implement that correctly though.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
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