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

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Message-ID: <CAKOOJTw90wcw=JZfXYGCrCK1GdxkRwgbjA5x5aKfBoE3GkW9jw@mail.gmail.com>
Date:   Tue, 1 Dec 2020 17:17:33 -0800
From:   Edwin Peer <edwin.peer@...adcom.com>
To:     Danielle Ratson <danieller@...dia.com>
Cc:     Michal Kubecek <mkubecek@...e.cz>, Jiri Pirko <jiri@...nulli.us>,
        Andrew Lunn <andrew@...n.ch>, 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>,
        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

On Tue, Dec 1, 2020 at 9:23 AM Danielle Ratson <danieller@...dia.com> wrote:

> The suggestions I have are:
> 1. Add a bit that for unknown media for each link (something like ETHTOOL_LINK_MODE_100000unknown_Full_BIT). I am not sure it is even possible or makes sense.
> 2. Pass the link mode as bitmap.
>
> Do you see any other option?

Other options include:

1) Let the user specify link encoding directly, as we do for FEC. This would
imply the number of lanes used at a given speed rather than the other way
around. Then you only need a handful of indices in the enum.

2) Instead of an enum, encode the semantics into the link mode bit
representation. N bits define the speed. Other bits define the encoding,
number of lanes, media, etc. This would solve the problem of decoding the
intent from a single user selected link mode index, but would require a v2
UABI. The user could have the same strings, but not much more. And then,
it's probably better to give each dimension their own field in a struct and be
done, lest we run out of bits. Let the user space tool map the link mode
string onto the appropriate struct values.

Regards,
Edwin Peer

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