netdev - Re: [RFC] micrel KSZ8041 disable auto negotiation with fiber

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Date:	Tue, 19 Jun 2012 18:08:29 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Aníbal Almeida Pinto <anibal.pinto@...cec.com>
CC:	<netdev@...r.kernel.org>
Subject: Re: [RFC] micrel KSZ8041 disable auto negotiation with fiber

On Tue, 2012-06-19 at 15:45 +0100, Aníbal Almeida Pinto wrote:
> Hi,
> 
> I am working on a custom board based on a OMAP L138 with a KSZ8041TL-FTL 
> phy that have fibber and copper support.
> 
> When using with fibber the board can't connect to a switch, only after 
> exec :
> 
> 	ethtool -s eth1 speed 100 duplex full autoneg off
> 
> the phy get link and start working.
> 
> On some switches it appears that autoneg don't work well with fibber, 
> ethtool reports that its at 10MB/s after exec
> 
> 	ethtool -s eth1 autoneg on

I'm not aware of any specification for autoneg over fibre, so I imagine
the PHY is being programmed with an invalid configuration and sending
weird signals.

> The auto negotiation bit on phy register is disable on start when using 
> the fibber but Linux don't appear to look at it.
> 
> Found a thread [1] that solve the problem but don't appear to be fully 
> accepted.
> 
> The problem is modifying the phy code without interfere with ethtool use.
> 
> Any official/accepted solution to this problem ?

The net driver or PHY driver needs to disable autoneg by default when
connected to fibre, and reject attempts to turn it on.

As for *how* the driver is supposed to know whether that's the case, I
have no idea...

> [1] - http://marc.info/?l=linuxppc-embedded&m=131107263711714

...which seems to be where the previous discussion ended.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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