netdev - Re: [PATCH net-next v3 2/7] ethtool: Get link mode in use instead of speed and duplex parameters

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Date:   Mon, 1 Feb 2021 16:14:05 -0800
From:   Edwin Peer <edwin.peer@...adcom.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Danielle Ratson <danieller@...dia.com>,
        Michal Kubecek <mkubecek@...e.cz>,
        netdev <netdev@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Jiri Pirko <jiri@...dia.com>, Andrew Lunn <andrew@...n.ch>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        mlxsw <mlxsw@...dia.com>, Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH net-next v3 2/7] ethtool: Get link mode in use instead of
 speed and duplex parameters

On Mon, Feb 1, 2021 at 2:20 PM Jakub Kicinski <kuba@...nel.org> wrote:

> > Should they not be the same thing?
>
> Okay. Does "supported modes" in ethtool for bnxt get ANDed with the
> supported modes of the plugged in module?
>
> What happens when no module is plugged in? List all?
>
> I've surveyed this behavior a few years back and three vendors I tested
> all had different interpretation on what to list in supported modes :/

Fair enough, I can't argue there. ;)

> > Yes, there would be multiple link modes that map to the same speed and
> > lane combination, but that doesn't mean you need to accept them if the
> > media doesn't match what's plugged in also. In the above scenario, the
> > supported mask should not list SR because CR is physically plugged in.
> > That way, the user knows what options are legal and the kernel knows
> > what it can reject.
>
> If the modes depend on what's plugged in - what happens if cable gets
> removed? We (you, Danielle, I) can agree what we think is best, but
> history teaches us that doesn't matter in long run. We had a similar
> conversation when it comes to FEC. There simply is no way for upstream
> developers to review the behavior is correct.

Given that supported is only defined in the context of autoneg today,
once could still specify. But again, you raise a fair concern.

The asymmetry in interface is still ugly though, you get to decide
which ugly is worse. :P

Regards,
Edwin Peer

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