linux-kernel - Re: [PATCH v9 3/7] mux: add help text for MULTIPLEXER config option

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Message-ID: <fcef2798-1645-41fb-952e-daf3657bc231@solid-run.com>
Date: Mon, 9 Feb 2026 11:31:31 +0000
From: Josua Mayer <josua@...id-run.com>
To: Peter Rosin <peda@...ntia.se>, Marc Kleine-Budde <mkl@...gutronix.de>,
	Vincent Mailhol <mailhol@...nel.org>, Vinod Koul <vkoul@...nel.org>, Neil
 Armstrong <neil.armstrong@...aro.org>, Aaro Koskinen <aaro.koskinen@....fi>,
	Andreas Kemnade <andreas@...nade.info>, Kevin Hilman <khilman@...libre.com>,
	Roger Quadros <rogerq@...nel.org>, Tony Lindgren <tony@...mide.com>, Janusz
 Krzysztofik <jmkrzyszt@...il.com>, Vignesh R <vigneshr@...com>, Andi Shyti
	<andi.shyti@...nel.org>, Ulf Hansson <ulf.hansson@...aro.org>, Rob Herring
	<robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
	<conor+dt@...nel.org>, Geert Uytterhoeven <geert+renesas@...der.be>, Magnus
 Damm <magnus.damm@...il.com>, Wolfram Sang <wsa+renesas@...g-engineering.com>
CC: Yazan Shhady <yazan.shhady@...id-run.com>, Jon Nettleton
	<jon@...id-run.com>, Mikhail Anikin <mikhail.anikin@...id-run.com>,
	"linux-can@...r.kernel.org" <linux-can@...r.kernel.org>,
	"linux-phy@...ts.infradead.org" <linux-phy@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH v9 3/7] mux: add help text for MULTIPLEXER config option

Hi Peter,

On 09/02/2026 13:10, Peter Rosin wrote:
> Hi!
>
> 2026-02-08 at 16:38, Josua Mayer wrote:
>> Add prompt and help text for CONFIG_MULTIPLEXER to allow enabling this
>> option thorugh the kernel configuration without explicit "select" driver
>> dependencies.
>>
>> Select it by default when COMPILE_TEST is set for better coverage.
>>
>> Signed-off-by: Josua Mayer <josua@...id-run.com>
>> ---
>>   drivers/mux/Kconfig | 9 ++++++++-
>>   1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/mux/Kconfig b/drivers/mux/Kconfig
>> index c68132e38138..4f7c6bb86fc6 100644
>> --- a/drivers/mux/Kconfig
>> +++ b/drivers/mux/Kconfig
>> @@ -4,7 +4,14 @@
>>   #
>>   
>>   config MULTIPLEXER
>> -	tristate
>> +	tristate "Generic Multiplexer Support"
>> +	default m if COMPILE_TEST
>> +	help
>> +	  This framework is designed to abstract multiplexer handling for
>> +	  devices via various GPIO-, MMIO/Regmap or specific multiplexer
>> +	  controller chips.
>> +
>> +	  If unsure, say no.
>>   
>>   menu "Multiplexer drivers"
>>   	depends on MULTIPLEXER
>>
> I'm not comfortable with making MULTIPLEXER a visible symbol. It is meant to
> be selected when needed (and there are a dozen or so instances). The kbuild
> docs has this on the subject:
>
> 	"In general use select only for non-visible symbols (no prompts
> 	 anywhere) and for symbols with no dependencies."
The patch description didn't make the decision logic clear,
and I plan to submit a standalone patch for this after v7.0-rc1.

Basically existing drivers using mux core used "select" to enable it,
even though the core can function standalone with device-tree.

Some of these users (phy-can-transceiver) function perfectly
perfectly fine without mux, and use it as an optional feature.

Likely drivers only used "select" to avoid writing helper functions,
prompt, kconfig description and stubs - which this patch-set added.

So I will argue that some existing users relying on "select" was wrong,
and that the mux framework is generally useful on its own.