netdev - Re: igb: question regarding auto-negotiation

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Date:	Thu, 4 Aug 2016 16:01:39 -0700
From:	Dominic Curran <dominic.curran@...rix.com>
To:	Alexander Duyck <alexander.duyck@...il.com>,
	"e1000-devel@...ts.sourceforge.net" 
	<e1000-devel@...ts.sourceforge.net>
CC:	Netdev <netdev@...r.kernel.org>
Subject: Re: igb: question regarding auto-negotiation



On 07/29/2016 09:35 PM, Alexander Duyck wrote:
> On Fri, Jul 29, 2016 at 4:37 PM, Dominic Curran
> <dominic.curran@...rix.com> wrote:
>> Hi
>>
>> This question refers to igb codebase.
>> I have a question regarding the setting of hw->mac.autoneg.
>>
>> Is it correct to say for igb driver:
>>     "if speed=1000 and duplex=FULL and media_type=COPPER  then  only
>> auto-negotiate enable is supported"
>>
>> i.e.
>>     with these settings (speed/duplex/media_type) then auto-negotiate can
>> _not_ be disabled.  Correct ?
>>
>> I say this for two reasons:
>> 1) The code in igb_set_spd_dplx() seems to indicate it:
>>
>>         case SPEED_1000 + DUPLEX_FULL:
>>                  mac->autoneg = 1;
>>                  adapter->hw.phy.autoneg_advertised = ADVERTISE_1000_FULL;
>>                  break;
>>
>> 2) Instrumenting the driver, I always see the autoneg code in
>> e1000_check_for_copper_link_generic()  get called after an igb_reset().
>>
>>
>> Have i understood correctly ?
>>
>> thanks in advance
>> dom
> If you are using copper then you are likely referring to 1000Base-T
> correct?  If so then autonegotation is a requirement.
>
> Here is the wikipedia URL that refers to this:
> https://en.wikipedia.org/wiki/Gigabit_Ethernet#1000BASE-T
>
> Hope this helps to clear it up.
>
> Thanks.
>
> - Alex

Thanks for reply.  I read the wiki link and a bunch of other links besides.

So I have a follow-up question:

You're right I am using copper and 1000Base-T, and as you say auto-neg 
is then requirement.

So why is it possible with the igb driver to set auto-neg to OFF ?

e.g.
# ethtool -a eth6
Pause parameters for eth6:
Autonegotiate:  on
RX:             on
TX:             on

Now turn it OFF:

# ethtool -A eth6 autoneg off

# ethtool -a eth6
Pause parameters for eth6:
Autonegotiate:  off
RX:             on
TX:             on

But added debug to the driver I _know_ that it is still 
auto-negotiating, and printing current settings indicates 
'Auto-negotiatiate' is on...

# ethtool  eth6
Settings for eth6:
         Supported ports: [ TP ]
         Supported link modes:   10baseT/Half 10baseT/Full
                                 100baseT/Half 100baseT/Full
                                 1000baseT/Full
         Supported pause frame use: No
         Supports auto-negotiation: Yes
         Advertised link modes:  10baseT/Half 10baseT/Full
                                 100baseT/Half 100baseT/Full
                                 1000baseT/Full
         Advertised pause frame use: No
         Advertised auto-negotiation: Yes
         Speed: 1000Mb/s
         Duplex: Full
         Port: Twisted Pair
         PHYAD: 1
         Transceiver: internal
         Auto-negotiation: on <<<<
         MDI-X: on
         Supports Wake-on: pumbg
         Wake-on: d
         Current message level: 0x00000007 (7)
                                drv probe link
         Link detected: yes

So I dont understand the difference between these two values ??
Can anyone help please ?

Thanks
dom