netdev - Re: lan78xx: /sys/class/net/eth0/carrier stuck at 1

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Message-ID: <20201023082959.496d4596@gollum>
Date:   Fri, 23 Oct 2020 08:29:59 +0200
From:   Juerg Haefliger <juerg.haefliger@...onical.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Juerg Haefliger <juerg.haefliger@...onical.com>,
        netdev@...r.kernel.org, woojung.huh@...rochip.com
Subject: Re: lan78xx: /sys/class/net/eth0/carrier stuck at 1

On Wed, 21 Oct 2020 21:35:48 +0200
Andrew Lunn <andrew@...n.ch> wrote:

> On Wed, Oct 21, 2020 at 05:00:53PM +0200, Juerg Haefliger wrote:
> > Hi,
> > 
> > If the lan78xx driver is compiled into the kernel and the network cable is
> > plugged in at boot, /sys/class/net/eth0/carrier is stuck at 1 and doesn't
> > toggle if the cable is unplugged and replugged.
> > 
> > If the network cable is *not* plugged in at boot, all seems to work fine.
> > I.e., post-boot cable plugs and unplugs toggle the carrier flag.
> > 
> > Also, everything seems to work fine if the driver is compiled as a module.
> > 
> > There's an older ticket for the raspi kernel [1] but I've just tested this
> > with a 5.8 kernel on a Pi 3B+ and still see that behavior.  
> 
> Hi Jürg

Hi Andrew,


> Could you check if a different PHY driver is being used when it is
> built and broken vs module or built in and working.
> 
> Look at /sys/class/net/eth0/phydev/driver

There's no such file.

 
> I'm wondering if in the builtin case, it is using genphy, but with
> modules it uses a more specific vendor driver.

Given that all works fine as long as the cable is unplugged at boot points
more towards a race at boot or incorrect initialization sequence or something.


...Juerg
 
> 	Andrew


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