linux-kernel - Re: [PATCH] net: fec: fix enet

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Date:	Mon, 30 Nov 2015 06:37:02 +0100
From:	Lothar Waßmann <LW@...O-electronics.de>
To:	Andrew Lunn <andrew@...n.ch>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Fabio Estevam <fabio.estevam@...escale.com>,
	Kevin Hao <haokexin@...il.com>,
	Lucas Stach <l.stach@...gutronix.de>,
	Nimrod Andy <B38611@...escale.com>,
	Philippe Reynes <tremyfr@...il.com>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, Stefan Agner <stefan@...er.ch>
Subject: Re: [PATCH] net: fec: fix enet_out clock handling

Hi,

> On Fri, Nov 27, 2015 at 02:39:10PM +0100, Lothar Waßmann wrote:
> > When ENET_OUT is being used as reference clock for an external PHY,
> > the clock must not be disabled while the PHY is active. Otherwise the
> > PHY may lose its internal state and require a reset to become
> > functional again.
> > 
> > A symptom for this bug is a network interface that constantly toggles
> > between UP and DOWN state:
> > fec 800f0000.ethernet eth0: Link is Up - 100Mbps/Full - flow control rx/tx
> > fec 800f0000.ethernet eth0: Link is Down
> > fec 800f0000.ethernet eth0: Link is Up - 100Mbps/Full - flow control rx/tx
> > fec 800f0000.ethernet eth0: Link is Down
> 
> Hi Lothar
> 
> When does this up/down happen? During normal operation when the link
> is administrative up?
> 
If booting with NFSROOT the rootfs cannot be mounted, because when the
interface is brought up the PHY starts toggling the link state.

> When did this start happening? Did it happen before 
> 8fff755e9f8d net: fec: Ensure clocks are enabled while using mdio bus
> 
No. The behaviour started exactly with this commit.

Lothar Waßmann
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