netdev - Re: [PATCH net-next 2/3] net: dp83869: Add ability to advertise Fiber connection

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Message-ID: <20200916221313.GI3526428@lunn.ch>
Date:   Thu, 17 Sep 2020 00:13:13 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Dan Murphy <dmurphy@...com>
Cc:     davem@...emloft.net, f.fainelli@...il.com, hkallweit1@...il.com,
        mkubecek@...e.cz, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 2/3] net: dp83869: Add ability to advertise
 Fiber connection

On Wed, Sep 16, 2020 at 03:54:34PM -0500, Dan Murphy wrote:
> Andrew
> 
> On 9/15/20 3:17 PM, Andrew Lunn wrote:
> > > +		linkmode_set_bit(ETHTOOL_LINK_MODE_100baseFX_Full_BIT,
> > > +				 phydev->supported);
> > > +		linkmode_set_bit(ETHTOOL_LINK_MODE_100baseFX_Half_BIT,
> > > +				 phydev->supported);
> > > +
> > > +		/* Auto neg is not supported in 100base FX mode */
> > Hi Dan
> > 
> > If it does not support auto neg, how do you decide to do half duplex?
> > I don't see any code here which allows the user to configure it.
> 
> Ethtool has the provisions to set the duplex and speed right?.

What i'm getting at is you say you support
ETHTOOL_LINK_MODE_100baseFX_Full_BIT &
ETHTOOL_LINK_MODE_100baseFX_Half_BIT. If there is no auto neg in FX
mode, i'm questioning how these two different modes code be used? I'm
guessing the PHY defaults to ETHTOOL_LINK_MODE_100baseFX_Full_BIT? How
does the user set it to ETHTOOL_LINK_MODE_100baseFX_Half_BIT?

> The only call back I see which is valid is config_aneg which would still
> require a user space tool to set the needed link modes.

Correct. Maybe all you need to do is point me at the code in the
driver which actually sets the PHY into half duplex in FX mode when
the user asks for it. Is it just clearing BMCR_FULLDPLX?

    Andrew