netdev - Re: Reporting SFP presence status

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Message-ID: <20201222142251.GJ3107610@lunn.ch>
Date:   Tue, 22 Dec 2020 15:22:51 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Martin Hundebøll <mhu@...icom.dk>
Cc:     netdev <netdev@...r.kernel.org>
Subject: Re: Reporting SFP presence status

On Tue, Dec 22, 2020 at 07:28:10AM +0100, Martin Hundebøll wrote:
> Hi Andrew,
> 
> On 21/12/2020 16.22, Andrew Lunn wrote:
> > On Mon, Dec 21, 2020 at 11:37:55AM +0100, Martin Hundebøll wrote:
> > > Hi Andrew,
> > > 
> > > I've browsed the code in drivers/net/phy, but haven't found a place where
> > > the SFP module status/change is reported to user-space. Is there a
> > > "standard" way to report insert/remove events for SFP modules, or should we
> > > just add a custom sysfs attribute to our driver?
> > 
> > Hi Martin
> > 
> > There is currently no standard way of notifying user space. But it is
> > something which could be added. But it should not be systfs. This
> > should be a netlink notification, probably as part of ethtool netlink
> > API. Or maybe the extended link info.
> > 
> > What is your intended use case? Why do you need to know when a module
> > has been inserted? It seems like you cannot do too much on such a
> > notification. It seems lots of modules don't conform to the standard,
> > will not immediately respond on the i2c bus. So ethtool -m is probably
> > not going to be useful. You probably need to poll until it does
> > respond, which defeats the purpose of having a notification.
> 
> You're right; a notification isn't what I need. But a way to query the
> current state of the module would be nice, i.e. using ethtool.

What do you mean by state? ethtool -m gives you some state
information. ENODEV gives you an idea that there is no module
inserted. Lots of data suggests there is a module. You can decode the
data to get a lot of information. 

There was also a patchset from Russell King a few weeks ago exposing
some information in debugfs. But since it is debugfs, you cannot rely
on it.

Back to, what is you real use cases here?

     Andrew