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

["Russell King (Oracle)" <linux@armlinux.org.uk>]

On Fri, Aug 01, 2025 at 03:04:31PM +0200, Csókás Bence wrote:
> Hi,
> 
> On 2025. 08. 01. 14:33, Russell King (Oracle) wrote:
> > 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@kernel.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.
> 
> The real question is: why on Earth is mdiobus_register_device() called
> _before_ the probe()?

Please review the code and *understand* it before making changes. This
is what any experienced programmer will do, so please get into that
habbit - it'll help you not to get a bad name in the kernel community.

If you don't understand that mdiobus_register_device() would be called
outside of the device's probe function, then you need to gain that
knowledge through research.

Please treat this as a learning exercise.

First step: grep -r mdiobus_register_device drivers/net/phy

Thanks.

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