netdev - Re: [PATCH net-next 1/6] ethtool: Extend link modes settings uAPI with lanes

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Date:   Sat, 17 Oct 2020 00:15:53 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Danielle Ratson <danieller@...dia.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, Ido Schimmel <idosch@...sch.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Jiri Pirko <jiri@...dia.com>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "mkubecek@...e.cz" <mkubecek@...e.cz>, mlxsw <mlxsw@...dia.com>,
        Ido Schimmel <idosch@...dia.com>,
        "johannes@...solutions.net" <johannes@...solutions.net>
Subject: Re: [PATCH net-next 1/6] ethtool: Extend link modes settings uAPI
 with lanes

> Example:
> - swp1 is a 200G port with 4 lanes.
> - QSFP28 is plugged in.
> - The user wants to select configuration of 100G speed using 2 lanes, 50G each.
> 
> $ ethtool swp1
> Settings for swp1:
>         Supported ports: [ FIBRE         Backplane ]
>         Supported link modes:   1000baseT/Full
>                                 10000baseT/Full
>                                 1000baseKX/Full
>                                 10000baseKR/Full
>                                 10000baseR_FEC
>                                 40000baseKR4/Full
>                                 40000baseCR4/Full
>                                 40000baseSR4/Full
>                                 40000baseLR4/Full
>                                 25000baseCR/Full
>                                 25000baseKR/Full
>                                 25000baseSR/Full
>                                 50000baseCR2/Full
>                                 50000baseKR2/Full
>                                 100000baseKR4/Full
>                                 100000baseSR4/Full
>                                 100000baseCR4/Full
>                                 100000baseLR4_ER4/Full
>                                 50000baseSR2/Full
>                                 10000baseCR/Full
>                                 10000baseSR/Full
>                                 10000baseLR/Full
>                                 10000baseER/Full
>                                 50000baseKR/Full
>                                 50000baseSR/Full
>                                 50000baseCR/Full
>                                 50000baseLR_ER_FR/Full
>                                 50000baseDR/Full

>                                 100000baseKR2/Full
>                                 100000baseSR2/Full
>                                 100000baseCR2/Full
>                                 100000baseLR2_ER2_FR2/Full
>                                 100000baseDR2/Full

I'm not sure i fully understand all these different link modes, but i
thought these 5 are all 100G using 2 lanes? So why cannot the user
simply do

ethtool -s swp1 advertise 100000baseKR2/Full

and the driver can figure out it needs to use two lanes at 50G?

    Andrew