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

[Danielle Ratson <danieller@nvidia.com>]

> -----Original Message-----
> From: Andrew Lunn <andrew@lunn.ch>
> Sent: Saturday, October 17, 2020 1:16 AM
> To: Danielle Ratson <danieller@nvidia.com>
> Cc: Jakub Kicinski <kuba@kernel.org>; Ido Schimmel <idosch@idosch.org>;
> netdev@vger.kernel.org; davem@davemloft.net; Jiri Pirko
> <jiri@nvidia.com>; f.fainelli@gmail.com; mkubecek@suse.cz; mlxsw
> <mlxsw@nvidia.com>; Ido Schimmel <idosch@nvidia.com>;
> johannes@sipsolutions.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

Hi Andrew,

Thanks for the feedback.

I guess you mean " ethtool -s swp1 advertise 100000baseKR2/Full on".

First, the idea might work but only for auto negotiation mode, whereas the lanes parameter is a solution for both.

Second, the command as you have suggested it, wouldn't change anything in the current situation as I checked. We can disable all the others and leave only the one we want but the command doesn't filter the other link modes but it just turns the mentioned link modes up if they aren't. However, the lanes parameter is a selector, which make it much more user friendly in my opinion.

Also, we can't turn only one of them up. But you have to set for example:

$ ethtool -s swp1 advertise 100000baseKR2/Full on 100000baseSR2/Full on 100000baseCR2/Full on 100000baseLR2_ER2_FR2/Full on 100000baseDR2/Full on

Am I missing something?