netdev - Re: phy link status not stable

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Message-ID: <CAGVrzcZ4BPJ-6t81vevb2g7jMqRmeCnGfEOhZA2gLO7qawZvPg@mail.gmail.com>
Date:	Tue, 16 Sep 2014 10:09:36 -0700
From:	Florian Fainelli <f.fainelli@...il.com>
To:	Mugunthan V N <mugunthanvnm@...com>
Cc:	netdev <netdev@...r.kernel.org>, David Miller <davem@...emloft.net>
Subject: Re: phy link status not stable

2014-09-16 9:26 GMT-07:00 Mugunthan V N <mugunthanvnm@...com>:
> Hi
>
> While doing ifdown/ifup test, phy link up status is very much delayed
> and also link up/down comes alternatively without physical link changes
> which leads to ifup failure. in v3.12 internal tree there is no failure.
> Pasting the logs below.

Assuming your driver calls phy_start() and phy_stop() from the
ndo_open() resp. ndo_stop() functions, these function calls are not
synchronous, as in they do not wait for the link to go UP resp. DOWN
before returning. The PHY state machine gets programmed to a new state
from phy_start() resp. phy_stop() and the next workqueue execution
will proceed with an actual state change.

>
> root@...37x-evm:~# ifup eth0
> [  652.633204] net eth0: initializing cpsw version 1.15 (0)
> [  652.717428] net eth0: phy found : id is : 0x221622
> udhcpc (v1.20.2) started
> Sending discover...
> Sending discover...
> [  658.717859] cpsw 4a100000.ethernet eth0: Link is Up - 1Gbps/Full -
> flow control rx/tx
> Sending discover...
> [  660.717894] cpsw 4a100000.ethernet eth0: Link is Down
> [  661.717937] cpsw 4a100000.ethernet eth0: Link is Up - 1Gbps/Full -
> flow control rx/tx
> No lease, failing
> root@...37x-evm:~# udhcpc
> udhcpc (v1.20.2) started
> Sending discover...
> Sending select for 172.24.190.6...
> Lease of 172.24.190.6 obtained, lease time 3600
> /etc/udhcpc.d/50default: Adding DNS 192.0.2.2
> /etc/udhcpc.d/50default: Adding DNS 192.0.2.3
> root@...37x-evm:~#
>
> Is this a known issue or any pointers where to look for clues?

This is not a known issue AFAICT, is the link really flapping? Not
sure if [1] could explain what you are seeing?

[1]: http://git.kernel.org/cgit/linux/kernel/git/davem/net.git/commit/?id=95e8b10393f88a0db88d97e9d1953f01c854315a
could ex

>
> Setup: TI-AM437x EVM
> Phy: Micrel KSZ9031 Gigabit PHY
>
> Thanks,
> Mugunthan V N
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-- 
Florian
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