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Message-ID: <20220415120147.7ya2rwtxcldahh4n@skbuf> Date: Fri, 15 Apr 2022 15:01:47 +0300 From: Vladimir Oltean <olteanv@...il.com> To: "Russell King (Oracle)" <linux@...linux.org.uk> Cc: Clément Léger <clement.leger@...tlin.com>, Andrew Lunn <andrew@...n.ch>, Vivien Didelot <vivien.didelot@...il.com>, Florian Fainelli <f.fainelli@...il.com>, "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Rob Herring <robh+dt@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Geert Uytterhoeven <geert+renesas@...der.be>, Magnus Damm <magnus.damm@...il.com>, Heiner Kallweit <hkallweit1@...il.com>, Thomas Petazzoni <thomas.petazzoni@...tlin.com>, Herve Codina <herve.codina@...tlin.com>, Miquèl Raynal <miquel.raynal@...tlin.com>, Milan Stevanovic <milan.stevanovic@...com>, Jimmy Lalande <jimmy.lalande@...com>, linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, linux-renesas-soc@...r.kernel.org, netdev@...r.kernel.org, Jean-Pierre Geslin <jean-pierre.geslin@....se.com>, Phil Edworthy <phil.edworthy@...esas.com> Subject: Re: [PATCH net-next 06/12] net: dsa: rzn1-a5psw: add Renesas RZ/N1 advanced 5 port switch driver On Fri, Apr 15, 2022 at 12:23:30PM +0100, Russell King (Oracle) wrote: > If ->shutdown has been called, the system is going down, and userspace > is probably already dead. There isn't anything preventing ->remove from being called after ->shutdown has been called. It all starts with the pattern that some driver authors prefer, which is to redirect their ->shutdown method to ->remove. They argue that it provides for a well-tested common path, so in turn, this pattern is quite widespread and I'm not one to argue for removing it. When such driver (redirecting ->shutdown to ->remove) is a bus driver (SPI, I2C, lately even the fsl-mc bus), the implication is that the controller will be unregistered on shutdown. To unregister a bus, you need to unregister all devices on the bus too. Due to implicit device ordering on the dpm_list, the ->shutdown() method of children on said bus has already executed, now we're in the context of the ->shutdown() procedure of the bus driver itself. You can argue "hey, that's SPI/I2C and this is a platform driver, there isn't any bus that unregisters on shutdown here", and you may have a point there. But platform devices aren't just memory-mapped devices, they can also be children of mfd devices on SPI/I2C buses. So in theory you can see this pattern happen on platform devices as well. This is the reason why I insist for uniformity in the DSA layer in the way that shutdown is handled. People copy and paste code a lot, and by leaving them with less variance in the code that they copy, subtle differences that are not understood but do matter are less likely to creep in.
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