linux-kernel - Re: [PATCH v9 3/6] mfd: Add RTL8231 core device

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Message-ID: <a26a5397-7597-49f6-9e73-3eb853915166@kernel.org>
Date: Fri, 26 Dec 2025 13:19:34 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Sander Vanheule <sander@...nheule.net>, kernel test robot
 <lkp@...el.com>, Lee Jones <lee@...nel.org>, Pavel Machek
 <pavel@...nel.org>, Linus Walleij <linus.walleij@...aro.org>,
 Michael Walle <mwalle@...nel.org>, Bartosz Golaszewski <brgl@...ev.pl>,
 Mark Brown <broonie@...nel.org>, Andrew Lunn <andrew@...n.ch>,
 Heiner Kallweit <hkallweit1@...il.com>, Russell King
 <linux@...linux.org.uk>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>
Cc: Paul Gazzillo <paul@...zz.com>,
 Necip Fazil Yildiran <fazilyildiran@...il.com>,
 oe-kbuild-all@...ts.linux.dev, linux-leds@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-gpio@...r.kernel.org, netdev@...r.kernel.org,
 Rob Herring <robh@...nel.org>, Conor Dooley <conor+dt@...nel.org>
Subject: Re: [PATCH v9 3/6] mfd: Add RTL8231 core device

On 26/12/2025 12:59, Sander Vanheule wrote:
> Adding the netdev and regmap maintainers for extra input.
> 
> On Mon, 2025-12-22 at 09:43 +0100, kernel test robot wrote:
>> url:    https://github.com/intel-lab-lkp/linux/commits/Sander-Vanheule/dt-bindings-leds-Binding-for-RTL8231-scan-matrix/20251216-015552
>> base:   https://git.kernel.org/pub/scm/linux/kernel/git/lee/mfd.git for-mfd-fixes
>> patch link:    https://lore.kernel.org/r/20251215175115.135294-4-sander%40svanheule.net
>> patch subject: [PATCH v9 3/6] mfd: Add RTL8231 core device
>> config: alpha-kismet-CONFIG_MDIO_BUS-CONFIG_REGMAP_MDIO-0-0 (https://download.01.org/0day-ci/archive/20251222/202512220956.FVakrdhV-lkp@intel.com/config)
>> reproduce: (https://download.01.org/0day-ci/archive/20251222/202512220956.FVakrdhV-lkp@intel.com/reproduce)
>>
> 
> For context: these patches introduce a new MFD with pinctrl and led subdevices.
> The RTL8231 MFD is attached to an MDIO bus, but it can also be attached to an
> I2C bus (not currently supported). The drivers use regmap to provide a bus
> abstraction.
> 
>> kismet warnings: (new ones prefixed by >>)
>>>> kismet: WARNING: unmet direct dependencies detected for MDIO_BUS when
>>>> selected by REGMAP_MDIO
>>    WARNING: unmet direct dependencies detected for MDIO_BUS
>>      Depends on [n]: NETDEVICES [=n]
>>      Selected by [y]:
>>      - REGMAP_MDIO [=y]
> 
> I'm a bit puzzled on how to solve this one. The issue detected here is that my
> driver (MFD_RTL8231) selects REGMAP_MDIO, which in turn selects MDIO_BUS. The
> latter is dependent on NETDEVICES, which is not selected in this test. 
> The kernel does not yet have any other consumers of REGMAP_MDIO, which is
> probably the reason the dependency issue has gone undetected until now.
> 
> REGMAP_MDIO is not a visible symbol, so it must be selected by drivers.

Reminds me old problem, probably the same:

https://lore.kernel.org/all/20250515140555.325601-2-krzysztof.kozlowski@linaro.org/

https://lore.kernel.org/all/20250516141722.13772-1-afd@ti.com/

Exactly the same MDIO here and there.

> 
> Other REGMAP_XYZ symbols (almost) exclusively use "depends on XYZ", but if I
> change REGMAP_MDIO to "depends on", the warning just changes to:
> 
>    WARNING: unmet direct dependencies detected for REGMAP_MDIO
>      Depends on [n]: MDIO_BUS [=n]
>      Selected by [y]:
>      - MFD_RTL8231 [=y] && HAS_IOMEM [=y]
> 
> Trying to make MFD_RTL8231 also depend on MDIO_BUS, like .e.g I2C dependent
> devices do, results in a recursive dependency:
> 
> 
>    error: recursive dependency detected!
>    	symbol GPIOLIB is selected by PINCTRL_RTL8231
>    	symbol PINCTRL_RTL8231 depends on MFD_RTL8231
>    	symbol MFD_RTL8231 depends on MDIO_BUS
>    	symbol MDIO_BUS is selected by PHYLIB
>    	symbol PHYLIB is selected by ARC_EMAC_CORE
>    	symbol ARC_EMAC_CORE is selected by EMAC_ROCKCHIP
>    	symbol EMAC_ROCKCHIP depends on OF_IRQ
>    	symbol OF_IRQ depends on IRQ_DOMAIN
>    	symbol IRQ_DOMAIN is selected by GENERIC_IRQ_CHIP
>    	symbol GENERIC_IRQ_CHIP is selected by GPIO_MVEBU
>    	symbol GPIO_MVEBU depends on GPIOLIB
>    
> The 'quick fix' appears to be to add "select NETDEVICES" to REGMAP_MDIO. The
> platforms that use the RTL8231 MFD are typically ethernet switches, so they
> would have NETDEVICES enabled anway, but that feels very heavy handed and
> automatically pulls in a lot of extra stuff. Would this be acceptable or is
> there a more desirable approach I'm not seeing here?

Rather fix the same way Andrew did it. Or maybe his patch was not merged?

Best regards,
Krzysztof