netdev - Re: [PATCH net] net: mdio_bus: Use devm for getting reset GPIO

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Message-ID: <aIy0HqFvCggTEyUk@shell.armlinux.org.uk>
Date: Fri, 1 Aug 2025 13:33:34 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Mark Brown <broonie@...nel.org>,
	Bence Csókás <csokas.bence@...lan.hu>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	"David S. Miller" <davem@...emloft.net>,
	Rob Herring <robh@...nel.org>, Andrew Lunn <andrew@...n.ch>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Csaba Buday <buday.csaba@...lan.hu>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net] net: mdio_bus: Use devm for getting reset GPIO

On Fri, Aug 01, 2025 at 02:25:17PM +0200, Geert Uytterhoeven wrote:
> Hi Mark,
> 
> On Fri, 1 Aug 2025 at 14:01, Mark Brown <broonie@...nel.org> wrote:
> > On Mon, Jul 28, 2025 at 05:34:55PM +0200, Bence Csókás wrote:
> > > Commit bafbdd527d56 ("phylib: Add device reset GPIO support") removed
> > > devm_gpiod_get_optional() in favor of the non-devres managed
> > > fwnode_get_named_gpiod(). When it was kind-of reverted by commit
> > > 40ba6a12a548 ("net: mdio: switch to using gpiod_get_optional()"), the devm
> > > functionality was not reinstated. Nor was the GPIO unclaimed on device
> > > remove. This leads to the GPIO being claimed indefinitely, even when the
> > > device and/or the driver gets removed.
> >
> > I'm seeing multiple platforms including at least Beaglebone Black,
> > Tordax Mallow and Libre Computer Alta printing errors in
> > next/pending-fixes today:
> >
> > [    3.252885] mdio_bus 4a101000.mdio:00: Resources present before probing
> >
> > Bisects are pointing to this patch which is 3b98c9352511db in -next,
> 
> My guess is that &mdiodev->dev is not the correct device for
> resource management.

No, looking at the patch, the patch is completely wrong.

Take for example mdiobus_register_gpiod(). Using devm_*() there is
completely wrong, because this is called from mdiobus_register_device().
This is not the probe function for the device, and thus there is no
code to trigger the release of the resource on unregistration.

Moreover, when the mdiodev is eventually probed, if the driver fails
or the driver is unbound, the GPIO will be released, but a reference
will be left behind.

Using devm* with a struct device that is *not* currently being probed
is fundamentally wrong - an abuse of devm.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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