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

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Date:   Mon, 30 Nov 2020 18:14:28 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     Edwin Peer <edwin.peer@...adcom.com>
Cc:     Ido Schimmel <idosch@...sch.org>, netdev <netdev@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, jiri@...dia.com,
        danieller@...dia.com, andrew@...n.ch, f.fainelli@...il.com,
        mkubecek@...e.cz, mlxsw@...dia.com,
        Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH net-next 1/6] ethtool: Extend link modes settings uAPI
 with lanes

Mon, Nov 30, 2020 at 06:01:43PM CET, edwin.peer@...adcom.com wrote:
>On Mon, Nov 23, 2020 at 1:40 AM Jiri Pirko <jiri@...nulli.us> wrote:
>
>> >Why can't this be implied by port break-out configuration? For higher
>> >speed signalling modes like PAM4, what's the difference between a
>> >port with unused lanes vs the same port split into multiple logical
>> >ports? In essence, the driver could then always choose the slowest
>>
>> There is a crucial difference. Split port is configured alwasy by user.
>> Each split port has a devlink instace, netdevice associated with it.
>> It is one level above the lanes.
>
>Right, but the one still implies the other. Splitting the port implies fewer
>lanes available.
>
>I understand the concern if the device cannot provide sufficient MAC
>resources to provide for the additional ports, but leaving a net device
>unused (with the option to utilize an additional, now spare, port) still
>seems better to me than leaving lanes unused and always wasted.

I don't follow what exactly are you implying. Could you elaborate a bit
more?

>
>Otherwise, the earlier suggestion of fully specifying the forced link
>mode (although I don't think Andrew articulated it quite that way)
>instead of a forced speed and separate lane mode makes most
>sense.
>
>Regards,
>Edwin Peer