netdev - Re: [PATCH 07/14] net: axienet: Fix SGMII support

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Message-ID: <20200110142038.2ed094ba@donnerap.cambridge.arm.com>
Date:   Fri, 10 Jan 2020 14:20:38 +0000
From:   Andre Przywara <andre.przywara@....com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Radhey Shyam Pandey <radhey.shyam.pandey@...inx.com>,
        Michal Simek <michal.simek@...inx.com>,
        Robert Hancock <hancock@...systems.ca>, netdev@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Russell King <rmk+kernel@....linux.org.uk>
Subject: Re: [PATCH 07/14] net: axienet: Fix SGMII support

On Fri, 10 Jan 2020 15:04:15 +0100
Andrew Lunn <andrew@...n.ch> wrote:

Hi Andrew,

> On Fri, Jan 10, 2020 at 11:54:08AM +0000, Andre Przywara wrote:
> > With SGMII, the MAC and the PHY can negotiate the link speed between
> > themselves, without the host needing to mediate between them.
> > Linux recognises this, and will call phylink's mac_config with the speed
> > member set to SPEED_UNKNOWN (-1).
> > Currently the axienet driver will bail out and complain about an
> > unsupported link speed.
> > 
> > Teach axienet's mac_config callback to leave the MAC's speed setting
> > alone if the requested speed is SPEED_UNKNOWN.  
> 
> Hi Andre
> 
> Is there an interrupt when SGMII signals a change in link state? If
> so, you should call phylink_mac_change().

Good point. The doc describes a "Auto-Negotiation Complete" interrupt status bit, which signal that " ... auto-negotiation of the SGMII or 1000BASE-X interface has completed."
But I have no clue whether that would trigger on a link status *change*. Is there a way to test this without pulling the cable? My board sits in a data centre, so is not easily accessible to me.

Cheers,
Andre.