linux-kernel - Re: [RFC PATCH net 4/5] net: dsa: microchip: ksz8863: be compatible with masters which unregister on shutdown

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Date:   Mon, 13 Sep 2021 09:51:00 -0700
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>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Woojung Huh <woojung.huh@...rochip.com>,
        UNGLinuxDriver@...rochip.com, 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>,
        Linus Walleij <linus.walleij@...aro.org>,
        George McCollister <george.mccollister@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Oleksij Rempel <linux@...pel-privat.de>,
        Michael Grzeschik <m.grzeschik@...gutronix.de>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Lino Sanfilippo <LinoSanfilippo@....de>
Subject: Re: [RFC PATCH net 4/5] net: dsa: microchip: ksz8863: be compatible
 with masters which unregister on shutdown



On 9/12/2021 5:09 AM, Vladimir Oltean wrote:
> Since commit 2f1e8ea726e9 ("net: dsa: link interfaces with the DSA
> master to get rid of lockdep warnings"), DSA gained a requirement which
> it did not fulfill, which is to unlink itself from the DSA master at
> shutdown time.
> 
> Since the Microchip sub-driver for KSZ8863 was introduced after the bad
> commit, it has never worked with DSA masters which decide to unregister
> their net_device on shutdown, effectively hanging the reboot process.
> To fix that, we need to call dsa_switch_shutdown.
> 
> Since this driver expects the MDIO bus to be backed by mdio_bitbang, I
> don't think there is currently any MDIO bus driver which implements its
> ->shutdown by redirecting it to ->remove, but in any case, to be
> compatible with that pattern, it is necessary to implement an "if this
> then not that" scheme, to avoid ->remove and ->shutdown from being
> called both for the same struct device.
> 
> Fixes: 60a364760002 ("net: dsa: microchip: Add Microchip KSZ8863 SMI based driver support")
> Link: https://lore.kernel.org/netdev/20210909095324.12978-1-LinoSanfilippo@gmx.de/
> Reported-by: Lino Sanfilippo <LinoSanfilippo@....de>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

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