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

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Message-ID: <87mtz4umxs.fsf@tarshish>
Date:   Thu, 26 Nov 2020 18:01:35 +0200
From:   Baruch Siach <baruch@...s.co.il>
To:     Andrew Lunn <andrew@...n.ch>
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

Hi Andrew,

On Thu, Nov 26 2020, Andrew Lunn wrote:
> On Thu, Nov 26, 2020 at 05:37:22PM +0200, Baruch Siach wrote:
>> 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?

I would like to report the port supported data rates to the system
user. I need to tell whether 10Gbps SFP module are supported in that
port in a generic way. The driver has this information. It is necessary
to implement the validate callback in phylink_mac_ops. But I see no way
to read this information from userspace.

> 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.

I understand that. I probably need a higher level concept of data rate
supported.

baruch

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