netdev - Cutting the link on ndo_stop - phy_stop or phy

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Date:   Tue, 4 Jun 2019 22:58:41 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     "linux@...linux.org.uk" <linux@...linux.org.uk>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "andrew@...n.ch" <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Cc:     Ioana Ciornei <ioana.ciornei@....com>
Subject: Cutting the link on ndo_stop - phy_stop or phy_disconnect?

Hi,

I've been wondering what is the correct approach to cut the Ethernet 
link when the user requests it to be administratively down (aka ip link 
set dev eth0 down).
Most of the Ethernet drivers simply call phy_stop or the phylink 
equivalent. This leaves an Ethernet link between the PHY and its link 
partner.
The Freescale gianfar driver (authored by Andy Fleming who also authored 
the phylib) does a phy_disconnect here. It may seem a bit overkill, but 
of the extra things it does, it calls phy_suspend where most PHY drivers 
set the BMCR_PDOWN bit. Only this achieves the intended purpose of also 
cutting the link partner's link on 'ip link set dev eth0 down'.
What is the general consensus here?
I see the ability to be able to put the PHY link administratively down a 
desirable feat. If it's left to negotiate/receive traffic etc while the 
MAC driver isn't completely set up and ready, in theory a lot of 
processing can happen outside of the operating system's control.

Regards,
-Vladimir