netdev - Re: [PATCH v2 net] net: dsa: mv88e6xxx: prevent interrupt storm caused by mv88e6390x_port_set

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Date:   Fri, 01 Mar 2019 21:37:27 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     hkallweit1@...il.com
Cc:     vivien.didelot@...il.com, andrew@...n.ch, f.fainelli@...il.com,
        netdev@...r.kernel.org
Subject: Re: [PATCH v2 net] net: dsa: mv88e6xxx: prevent interrupt storm
 caused by mv88e6390x_port_set_cmode

From: Heiner Kallweit <hkallweit1@...il.com>
Date: Thu, 28 Feb 2019 07:39:15 +0100

> When debugging another issue I faced an interrupt storm in this
> driver (88E6390, port 9 in SGMII mode), consisting of alternating
> link-up / link-down interrupts. Analysis showed that the driver
> wanted to set a cmode that was set already. But so far
> mv88e6390x_port_set_cmode() doesn't check this and powers down
> SERDES, what causes the link to break, and eventually results in
> the described interrupt storm.
> 
> Fix this by checking whether the cmode actually changes. We want
> that the very first call to mv88e6390x_port_set_cmode() always
> configures the registers, therefore initialize port.cmode with
> a value that is different from any supported cmode value.
> We have to take care that we only init the ports cmode once
> chip->info->num_ports is set.
> 
> v2:
> - add small helper and init the number of actual ports only
> 
> Fixes: 364e9d7776a3 ("net: dsa: mv88e6xxx: Power on/off SERDES on cmode change")
> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>

Applied, and queued up for -stable.

Thanks.