netdev - Re: Get MAC supported link modes for SFP port

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Message-ID: <20201126154716.GN2073444@lunn.ch>
Date:   Thu, 26 Nov 2020 16:47:16 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Baruch Siach <baruch@...s.co.il>
Cc:     netdev@...r.kernel.org, Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>
Subject: Re: Get MAC supported link modes for SFP port

On Thu, Nov 26, 2020 at 05:37:22PM +0200, Baruch Siach wrote:
> Hi netdev list,
> 
> I am trying to retrieve all MAC supported link modes
> (ETHTOOL_LINK_MODE_*) for network interfaces with SFP port. The
> 'supported' bit mask that ETHTOOL_GLINKSETTINGS provides in
> link_mode_masks[] changes to match the SFP module that happens to be
> plugged in. When no SFP module is plugged, the bit mask looks
> meaningless.

That sounds like it is doing the correct thing.

> I understand that ETHTOOL_LINK_MODE_* bits are meant to describe PHY
> level capabilities. So I would settle for a MAC level "supported rates"
> list.

What is your use cases?

A MAC without some form a PHY, be it copper, fibre, or a faked
fixed-link, is useless. You need the combination of what the MAC can
do and what the PHY can do to have any meaning information.

       Andrew