Re: igb: question regarding auto-negotiation

[Dominic Curran]

On 07/29/2016 09:35 PM, Alexander Duyck wrote:
On Fri, Jul 29, 2016 at 4:37 PM, Dominic Curran
<dominic.cur...@citrix.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