netdev - Re: [RFC PATCH 12/16] dsa: Make mdio bus optional

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Date:	Fri, 27 May 2016 12:38:47 -0400
From:	Vivien Didelot <vivien.didelot@...oirfairelinux.com>
To:	Andrew Lunn <andrew@...n.ch>
Cc:	netdev <netdev@...r.kernel.org>,
	Florian Fainelli <f.fainelli@...il.com>,
	John Crispin <john@...ozen.org>, Bryan.Whitehead@...rochip.com
Subject: Re: [RFC PATCH 12/16] dsa: Make mdio bus optional

Hi Andrew,

Andrew Lunn <andrew@...n.ch> writes:

> On Fri, May 27, 2016 at 10:55:45AM -0400, Vivien Didelot wrote:
>> Hi Andrew,
>> 
>> Andrew Lunn <andrew@...n.ch> writes:
>> 
>> > -	mdiobus_unregister(ds->slave_mii_bus);
>> > +	if (ds->slave_mii_bus && ds->drv->phy_read)
>> > +		mdiobus_unregister(ds->slave_mii_bus);
>> 
>> So if a driver registered the slave MII bus itself, it may have
>> unregistered it itself as well, so checking ds->slave_mii_bus is OK
>> (assuming the driver correctly zero'ed it).
>> 
>> But is it necessary to check ds->drv->phy_read?
>
> It makes the code symmetrical to the register code, which makes the
> same check. My experience is that keeping the code symmetrical results
> in less surprises late on.
>
> One such surprise could be a driver that does not zero
> ds->slave_mii_bus. In fact, mv88e6xxx does not zero it. So we would
> get a double unregister happening. We also don't want the core
> unregistering it, since we have other cleanup work to do, we have an
> of_node_put() to call.

OK good for me, as long as it is intuitive for the driver
implementation.

Thanks,

        Vivien