netdev - Re: How to toggle physical link via ethtool

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Message-ID: <20210421103012.45a3a64a@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Wed, 21 Apr 2021 10:30:12 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Sunil Kovvuri <sunil.kovvuri@...il.com>
Cc:     Linux Netdev List <netdev@...r.kernel.org>,
        Andrew Lunn <andrew@...n.ch>,
        Sunil Goutham <sgoutham@...vell.com>
Subject: Re: How to toggle physical link via ethtool

On Wed, 21 Apr 2021 18:12:16 +0530 Sunil Kovvuri wrote:
> Hi,
> 
> Have a query on how to bring down physical link (serdes) for a NIC interface.
> 
> I am under assumption that for a SR-IOV NIC, when user executes
> "ifconfig eth-pf down",
> it should not bring down physical link as there could be virtual
> interfaces still active.
> Let me know if this assumption itself is wrong.

How VFs operate is really implementation specific, so it'd be
interesting to hear from the vendors but IIUC bringing PF down 
should shut down the link.

What usually keeps the link up is stuff like NC-SI, but not VFs.

> If the assumption is correct and if user wants to intentionally bring
> down physical link for
> whatever reasons, then I do not see a way to do this. There are no
> commands either in
> 'ethtool' or 'ip link' to achieve this.
> 
> Would it be okay to add a ethtool command similar to 'ethtool
> --identify" to toggle physical link.