netdev - Re: [PATCH] net: macb: do not disable MDIO bus when closing interface

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Message-ID: <20180809151433.GB20006@lunn.ch>
Date:   Thu, 9 Aug 2018 17:14:33 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Anssi Hannula <anssi.hannula@...wise.fi>
Cc:     Claudiu Beznea <Claudiu.Beznea@...rochip.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] net: macb: do not disable MDIO bus when closing interface

Hi Anssi

> macb_reset_hw() is called in init path too, though, so maybe clearing
> all bits is intentional / wanted to get the controller to a known state,
> even though the comment only mentions TX/RX?

You need to be careful here. Once of_mdiobus_register() is called, the
MDIO should be usable. If you happen to have an Ethernet switch on the
bus, it could be probed then. The DSA driver will start using the bus.
Or if you have a second PHY, connected to some other MAC, it could be
used by the other MAC.  This all happens in the macb_probe function.

Sometime later, the interface will be up'ed. At this point macb_open()
is called, which calls macb_init_hw(), which calls
macb_reset_hw(). What you don't want happening is changes to the NCR
at this point breaking an MDIO transaction which might be going on.

Ideally, the MPE should be enabled before of_mdiobus_register(), and
left alone until mdiobus_unregister() is called in macb_remove().

     Andrew