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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Message-ID: <20240104154927.dq3bsbzu55qefsqo@skbuf>
Date: Thu, 4 Jan 2024 17:49:27 +0200
From: Vladimir Oltean <vladimir.oltean@....com>
To: Alvin Šipraga <ALSI@...g-olufsen.dk>
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 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.