netdev - Re: [Question] Return value of mii

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Message-ID: <8cbd4650-aeed-4d1c-8173-957776dfec51@gmail.com>
Date: Fri, 21 Nov 2025 07:53:21 +0100
From: Heiner Kallweit <hkallweit1@...il.com>
To: Buday Csaba <buday.csaba@...lan.hu>, netdev@...r.kernel.org
Subject: Re: [Question] Return value of mii_bus->write()

On 11/21/2025 7:31 AM, Buday Csaba wrote:
> I am preparing a patch to eliminate kernel-doc warnings in mdio_device.c
> and mdio_bus.c
> 
> I have ran into an ambiguity: what is mii_bus->write() supposed to
> return on success? Documentation/networking/phy.txt does not give any
> information about it, neither does the kdoc in include/linux/phy.h.
> 
> It is clear that 0 is treated as success, and a negative indicates
> failure. The reference implementation also follows this convention.
> But the code in mdio_bus.c, for example: __mdiobus_modify_changed(),
> seems to also expect positive return values from write().
> 
I think you misread the code. __mdiobus_modify_changed() returns
a positive value in case new and old value differ, but __mdiobus_write()
never returns a positive value.

> Is there any other implementation that allows positive return
> values for success? Should it be mentioned in kernel-doc?
> 
> Thanks,
> Csaba
> 
>