netdev - Re: PROBLEM: XGBE unable to autoneg when advertising only 1GbE KX mode

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Message-ID: <BN0PR08MB6951A0758F4983512A99018383D09@BN0PR08MB6951.namprd08.prod.outlook.com>
Date:   Thu, 19 May 2022 19:02:18 +0000
From:   "Pighin, Anthony (Nokia - CA/Ottawa)" <anthony.pighin@...ia.com>
To:     "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "Shyam-sundar.S-k@....com" <Shyam-sundar.S-k@....com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Pighin, Anthony (Nokia - CA/Ottawa)" <anthony.pighin@...ia.com>
Subject: Re: PROBLEM: XGBE unable to autoneg when advertising only 1GbE KX
 mode

(Consolidating the two threads; adding even more asymmetric results)

Additional information:

I performed an asymmetric test. One side has 'ethtool -s bp3 advertise 0x20000' and the other side of the link has 'ethtool -s bp3 advertise 0xa0000' (ie. one side is advertising 1G only, the other is advertising 1G+10G). If I bring up the 1G-only side first, followed by the 1G+10G side, then the link properly comes up at 1G. However, if I do the reverse, and bring up the 1G+10G side first, followed by the 1G-only side, there is no link up. I need to bounce the 1G+10G side again (ip set link bp3 down/up) to get the link to come up.

I then performed a second asymmetric test. One side had 'ethtool -s bp3 0x120000' and the other side of the link has 'ethtool -s bp3 advertise 0xa0000' (ie. both sides have 1G+10G, but the 10G differ between FEC and non-FEC). This means the common denominator is the 1G speed. In this case, no matter what side of the link I brought up first, they linked up at 1G.

So it appears that either two speeds need to be advertised, or that at least one 10G speed needs to be advertised, even if it doesn't match in the end.

The setup is two identical systems using the XGBE in backplane mode for inter-system communications (redundancy). The processor itself is a Zen (Family 23, Model 1, Stepping 2).