netdev - Re: [PATCH net-next 1/2] net: phy: unregister MDIO bus in _devm_mdiobus

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Date:   Wed, 19 Feb 2020 23:21:03 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        David Miller <davem@...emloft.net>,
        Realtek linux nic maintainers <nic_swsd@...ltek.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 1/2] net: phy: unregister MDIO bus in
 _devm_mdiobus_free if needed

On Mon, Feb 17, 2020 at 09:34:57PM +0100, Heiner Kallweit wrote:
> If using managed MDIO bus handling (devm_mdiobus_alloc et al) we still
> have to manually unregister the MDIO bus. For drivers that don't depend
> on unregistering the MDIO bus at a specific, earlier point in time we
> can make driver author's life easier by automagically unregistering
> the MDIO bus. This extension is transparent to existing drivers.
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
> ---
>  drivers/net/phy/mdio_bus.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
> index 9bb9f37f2..6af51cbdb 100644
> --- a/drivers/net/phy/mdio_bus.c
> +++ b/drivers/net/phy/mdio_bus.c
> @@ -170,7 +170,12 @@ EXPORT_SYMBOL(mdiobus_alloc_size);
>  
>  static void _devm_mdiobus_free(struct device *dev, void *res)
>  {
> -	mdiobus_free(*(struct mii_bus **)res);
> +	struct mii_bus *bus = *(struct mii_bus **)res;
> +
> +	if (bus->state == MDIOBUS_REGISTERED)
> +		mdiobus_unregister(bus);
> +
> +	mdiobus_free(bus);
>  }

Hi Heiner

The API is rather asymmetric. The alloc is not just setting up a free,
but also an unregister. Are there other examples of this in the
kernel?

Maybe a devm_of_mdiobus_register() would be better? It is then clear
that the unregister happens because of this call, and the free because
of the devm_mdiobus_alloc().

   Andrew