netdev - Re: [PATCH net-next 05/10] net: dsa: qca8k: skip MDIO bus creation if its OF node has status = "disabled"

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Date: Thu, 4 Jan 2024 16:04:52 +0000
From: Alvin Šipraga <ALSI@...g-olufsen.dk>
To: Vladimir Oltean <vladimir.oltean@....com>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "David S. Miller"
	<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Andrew Lunn
	<andrew@...n.ch>, Florian Fainelli <f.fainelli@...il.com>, Luiz Angelo Daros
 de Luca <luizluca@...il.com>, Linus Walleij <linus.walleij@...aro.org>,
	Florian Fainelli <florian.fainelli@...adcom.com>, Hauke Mehrtens
	<hauke@...ke-m.de>, Christian Marangi <ansuelsmth@...il.com>,
	Arınç ÜNAL <arinc.unal@...nc9.com>
Subject: Re: [PATCH net-next 05/10] net: dsa: qca8k: skip MDIO bus creation if
 its OF node has status = "disabled"

On Thu, Jan 04, 2024 at 05:49:27PM +0200, Vladimir Oltean wrote:
> On Thu, Jan 04, 2024 at 03:44:48PM +0000, Alvin Šipraga wrote:
> > On Thu, Jan 04, 2024 at 04:00:32PM +0200, Vladimir Oltean wrote:
> > > Currently the driver calls the non-OF devm_mdiobus_register() rather
> > > than devm_of_mdiobus_register() for this case, but it seems to rather
> > > be a confusing coincidence, and not a real use case that needs to be
> > > supported.
> > 
> > I am not really sure about the use case, but I always thought that
> > status = "disabled" sort of functions the same as if the node were
> > simply never specified. But with your change, there is a behavioural
> > difference between these two cases:
> > 
> >   (a) mdio unspecified => register "qca8k-legacy user mii"
> >   (b) mdio specified, but status = "disabled" => don't register anything
> > 
> > Was this your intention?
> 
> Yeah, it was my intention. I'm not sure if I agree with your equivalence.
> For example, PCI devices probe through enumeration. Their OF node is
> optional, aka when absent, they still probe. But when an associated OF
> node exists and has status = "disabled", they don't probe.

Yes, good example with PCIe. The change makes sense then. Thanks for clarifying.