netdev - net: phy: micrel KSZ9031 ifdown ifup issue

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Date:   Fri, 13 Sep 2019 10:42:38 -0400
From:   Paul Thomas <pthomas8589@...il.com>
To:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: net: phy: micrel KSZ9031 ifdown ifup issue

Hello,

I think I'm seeing an issue with the PHY hardware or PHY driver. What
happens is sometimes (but not always) when I do 'ip link set eth0
down' followed by 'ip link set eth0 up' I don't ever see an
auto-negotiation again. LEDs don't come on, ethtool reports 'Link
detected: no'. Even physically unplugging and plugging the network
cable doesn't bring it back. I have to do a reboot to get the
networking back.

When the networking is started I don't see any issue forcing
negotiations by unplugging and plugging the cable. I get standard
messages like this all day long:
[   21.031793] 003: macb ff0b0000.ethernet eth0: link down
[   26.142835] 003: macb ff0b0000.ethernet eth0: link up (1000/Full)

One thing that makes me think this is the PHY is that we have another
Ethernet port using the DP83867 PHY and I can always do ifdown/ifup
with it.

This is using a 5.2.10 kernel on arm64 zynqmp platform with the macb driver.

Is this something anyone else has seen? I know there is some Errata
with this part, but I'm hoping there is something to fix or work
around this. Any thoughts on where to look or add debugging would
appreciated.

thanks,
Paul