netdev - Re: Debugging Ethernet issues

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Date:   Sun, 13 Nov 2016 11:55:15 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Mason <slash.tmp@...e.fr>, Andrew Lunn <andrew@...n.ch>
Cc:     netdev <netdev@...r.kernel.org>, Mans Rullgard <mans@...sr.com>,
        Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Zach Brown <zach.brown@...com>,
        Shaohui Xie <shaohui.xie@....com>,
        Tim Beale <tim.beale@...iedtelesis.co.nz>,
        Brian Hill <brian@...ston-radar.com>,
        Vince Bridgers <vbridgers2013@...il.com>,
        Balakumaran Kannan <kumaran.4353@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Sebastian Frias <sf84@...oste.net>,
        Kirill Kapranov <kapranoff@...ox.ru>
Subject: Re: Debugging Ethernet issues

Le 13/11/2016 à 11:51, Mason a écrit :
> On 13/11/2016 04:09, Andrew Lunn wrote:
> 
>> Mason wrote:
>>
>>> When connected to a Gigabit switch
>>> 3.4 negotiates a LAN DHCP setup instantly
>>> 4.7 requires over 5 seconds to do so
>>
>> When you run tcpdump on the DHCP server, are you noticing the first
>> request is missing?
>>
>> What can happen is the dhclient gets started immediately and sends out
>> its first request before auto-negotiation has finished. So this first packet
>> gets lost. The retransmit after a few seconds is then successful.
> 
> I will run tcpdump on the server as I run udhcpc on the client
> for Linux 3.4 vs 4.7
> 
> Do you know what would make auto-negotiation fail at 100 Mbps
> on 4.7? (whereas it succeeds on 3.4)
> 
> (Thinking out loud) If the problem were in auto-negotiation,
> then if should work if I hard-code speed and duplex using
> ethtool, right? (IIRC, hard-coding doesn't help.)

I would start with checking basic things:

- does your Ethernet driver get a link UP being reported correctly
(netif_carrier_ok returns 1)?
- if you let the bootloader configure the PHY and utilize the Generic
PHY driver instead of the Atheros PHY driver, does the problem appear as
well?
- what do transmit/receive counters on the Ethernet driver/MAC return?
-- 
Florian