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

[Peter Rosin]

Hi!

2026-02-09 at 12:31, Josua Mayer wrote:
> 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 at solid-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.

When I wrote the mux sub-system it was very much intentional and by
design that drivers needing a mux should select MULTIPLEXER, and that
MULTIPLEXER should not be a visible symbol.

You say that it could be useful to have it visible, which is all fine
I suppose. But, you fail to address that quote from the kbuild docs.
Why is it OK to have the preexisting drivers select a visible symbol,
when the kbuild documentation states that it should not be done that
way?

Cheers,
Peter