netdev - Re: [PATCH net 5/7] net: dsa: seville: register the mdiobus under devres

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Message-ID: <18635376-118f-4f98-74b5-6dbe81f893d9@gmail.com>
Date:   Mon, 7 Feb 2022 18:48:40 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Vladimir Oltean <vladimir.oltean@....com>, netdev@...r.kernel.org
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        DENG Qingfang <dqfext@...il.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        UNGLinuxDriver@...rochip.com,
        Oleksij Rempel <linux@...pel-privat.de>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Laurentiu Tudor <laurentiu.tudor@....com>,
        Rafael Richter <rafael.richter@....de>,
        Daniel Klauer <daniel.klauer@....de>
Subject: Re: [PATCH net 5/7] net: dsa: seville: register the mdiobus under
 devres



On 2/7/2022 8:15 AM, Vladimir Oltean wrote:
> As explained in commits:
> 74b6d7d13307 ("net: dsa: realtek: register the MDIO bus under devres")
> 5135e96a3dd2 ("net: dsa: don't allocate the slave_mii_bus using devres")
> 
> mdiobus_free() will panic when called from devm_mdiobus_free() <-
> devres_release_all() <- __device_release_driver(), and that mdiobus was
> not previously unregistered.
> 
> The Seville VSC9959 switch is a platform device, so the initial set of
> constraints that I thought would cause this (I2C or SPI buses which call
> ->remove on ->shutdown) do not apply. But there is one more which
> applies here.
> 
> If the DSA master itself is on a bus that calls ->remove from ->shutdown
> (like dpaa2-eth, which is on the fsl-mc bus), there is a device link
> between the switch and the DSA master, and device_links_unbind_consumers()
> will unbind the seville switch driver on shutdown.
> 
> So the same treatment must be applied to all DSA switch drivers, which
> is: either use devres for both the mdiobus allocation and registration,
> or don't use devres at all.
> 
> The seville driver has a code structure that could accommodate both the
> mdiobus_unregister and mdiobus_free calls, but it has an external
> dependency upon mscc_miim_setup() from mdio-mscc-miim.c, which calls
> devm_mdiobus_alloc_size() on its behalf. So rather than restructuring
> that, and exporting yet one more symbol mscc_miim_teardown(), let's work
> with devres and replace of_mdiobus_register with the devres variant.
> When we use all-devres, we can ensure that devres doesn't free a
> still-registered bus (it either runs both callbacks, or none).
> 
> Fixes: ac3a68d56651 ("net: phy: don't abuse devres in devm_mdiobus_register()")
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
-- 
Florian