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

[Juerg Haefliger <juerg.haefliger@canonical.com>]

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On Fri, 23 Oct 2020 15:05:19 +0200
Andrew Lunn <andrew@lunn.ch> wrote:

> On Fri, Oct 23, 2020 at 08:29:59AM +0200, Juerg Haefliger wrote:
> > On Wed, 21 Oct 2020 21:35:48 +0200
> > Andrew Lunn <andrew@lunn.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 _think_ that means it is using genphy, the generic PHY driver, not a
> specific vendor PHY driver? What does
> 
> /sys/class/net/eth0/phydev/phy_id contain.

There is no directory /sys/class/net/eth0/phydev.

$ ls /sys/class/net/eth0/
addr_assign_type  broadcast        carrier_down_count  dev_port  duplex             ifalias  link_mode         netdev_group  phys_port_name  proto_down  statistics    type
addr_len          carrier          carrier_up_count    device    flags              ifindex  mtu               operstate     phys_switch_id  queues      subsystem     uevent
address           carrier_changes  dev_id              dormant   gro_flush_timeout  iflink   name_assign_type  phys_port_id  power           speed       tx_queue_len


> > 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.  
> 
> Could be. Could you run
> 
> mii-tool -vv eth0

Hrm. Running that command unlocks the carrier flag and it starts toggling on
cable unplug/plug. First invocation:

$ sudo mii-tool -vv eth0
Using SIOCGMIIPHY=0x8947
eth0: negotiated 1000baseT-FD flow-control, link ok
  registers for MII PHY 1: 
    1040 79ed 0007 c132 05e1 cde1 000f 0000
    0000 0200 0800 0000 0000 0000 0000 3000
    0000 0000 0088 0000 0000 0000 3200 0004
    0040 a000 a000 0000 a035 0000 0000 0000
  product info: vendor 00:01:f0, model 19 rev 2
  basic mode:   autonegotiation enabled
  basic status: autonegotiation complete, link ok
  capabilities: 1000baseT-FD 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
  advertising:  1000baseT-FD 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control
  link partner: 1000baseT-FD 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control

Subsequent invocation:

$ sudo mii-tool -vv eth0
Using SIOCGMIIPHY=0x8947
eth0: negotiated 1000baseT-FD flow-control, link ok
  registers for MII PHY 1: 
    1040 79ed 0007 c132 05e1 cde1 000d 0000
    0000 0200 0800 0000 0000 0000 0000 3000
    0000 0000 0088 0000 0000 0000 3200 0004
    0040 a000 0000 0000 a035 0000 0000 0000
  product info: vendor 00:01:f0, model 19 rev 2
  basic mode:   autonegotiation enabled
  basic status: autonegotiation complete, link ok
  capabilities: 1000baseT-FD 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
  advertising:  1000baseT-FD 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control
  link partner: 1000baseT-FD 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control

In the first invocation, register 0x1a shows a pending link-change interrupt
(0xa000) which wasn't serviced (and cleared) for some reason. Dumping the
registers cleared that interrupt bit and things start working correctly
afterwards. Nor sure yet why that first interrupt is ignored.

...Juerg

 
> in the good and bad case.
> 
>    Andrew
> 


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