netdev - Re: IMX6 FEC connection drops occasionally with 'MDIO read timeout'

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Message-ID: <20170407160915.GF23415@lunn.ch>
Date:   Fri, 7 Apr 2017 18:09:15 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Tim Harvey <tharvey@...eworks.com>
Cc:     netdev <netdev@...r.kernel.org>,
        Fabio Estevam <fabio.estevam@....com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Fugang Duan <fugang.duan@....com>,
        Koen Vandeputte <koen.vandeputte@...ntric.com>
Subject: Re: IMX6 FEC connection drops occasionally with 'MDIO read timeout'

On Fri, Apr 07, 2017 at 07:47:17AM -0700, Tim Harvey wrote:
> Greetings,
> 
> I've had a couple of users report that they are getting occasional
> link drops when using IMX6 FEC on our boards which are using a Marvell
> 88E1510 PHY:
> 
> [ 9348.474418] fec 2188000.ethernet eth0: MDIO read timeout
> [ 9350.478804] fec 2188000.ethernet eth0: Link is Down
> 
> If they bring the interface back up it works fine.
> 
> The most recent version of Linux they have tested and seen this on is
> v4.9 with CONFIG_MARVELL_PHY=y
> 
> Has anyone else run into this or know what the issue could be? Should
> there be any retries at the MDIO level or above?

Hi Tim

MDIO is assumed to be reliable. It failing is bad.

However, ETIMEOUT is interesting. The MDIO protocol has no flow
control. There is no way for the PHY to delay replying.

I would suggest you look at the power management code. What i have
seen with the FEC, when using switches attached to the FEC, is that if
the clocks are turned off, you get ETIMEOUT from MDIO.

    Andrew