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: <ajlbpd63vpgkyvzflimq7qbzrdvgqizbg6qwj32qudd4ibgywm@ckdcvnsrm23u>
Date: Thu, 4 Jan 2024 15:44:48 +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 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?

> 
> If the device tree says status = "disabled" for the MDIO bus, we
> shouldn't need an MDIO bus at all. Instead, just exit as early as
> possible and do not call any MDIO API.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> ---
>  drivers/net/dsa/qca/qca8k-8xxx.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/dsa/qca/qca8k-8xxx.c b/drivers/net/dsa/qca/qca8k-8xxx.c
> index 5f47a290bd6e..21e36bc3c015 100644
> --- a/drivers/net/dsa/qca/qca8k-8xxx.c
> +++ b/drivers/net/dsa/qca/qca8k-8xxx.c
> @@ -949,9 +949,11 @@ qca8k_mdio_register(struct qca8k_priv *priv)
>  	struct dsa_switch *ds = priv->ds;
>  	struct device_node *mdio;
>  	struct mii_bus *bus;
> -	int err;
> +	int err = 0;
>  
>  	mdio = of_get_child_by_name(priv->dev->of_node, "mdio");
> +	if (mdio && !of_device_is_available(mdio))
> +		goto out;
>  
>  	bus = devm_mdiobus_alloc(ds->dev);
>  	if (!bus) {
> @@ -967,7 +969,7 @@ qca8k_mdio_register(struct qca8k_priv *priv)
>  	ds->user_mii_bus = bus;
>  
>  	/* Check if the devicetree declare the port:phy mapping */
> -	if (of_device_is_available(mdio)) {
> +	if (mdio) {
>  		bus->name = "qca8k user mii";
>  		bus->read = qca8k_internal_mdio_read;
>  		bus->write = qca8k_internal_mdio_write;
> @@ -986,7 +988,7 @@ qca8k_mdio_register(struct qca8k_priv *priv)
>  
>  out_put_node:
>  	of_node_put(mdio);
> -
> +out:
>  	return err;
>  }
>  
> -- 
> 2.34.1
>