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

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Message-ID: <20201021193548.GU139700@lunn.ch>
Date:   Wed, 21 Oct 2020 21:35:48 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Juerg Haefliger <juerg.haefliger@...onical.com>
Cc:     netdev@...r.kernel.org, woojung.huh@...rochip.com
Subject: Re: lan78xx: /sys/class/net/eth0/carrier stuck at 1

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

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

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

	Andrew