Re: [PATCH v10 8/9] mux: add prompt and help text to CONFIG_MULTIPLEXER making it visible

[Ulf Hansson]

On Wed, 25 Feb 2026 at 12:35, Josua Mayer <josua@xxxxxxxxxxxxx> wrote:
>
> The multiplexer subsystem was initially designed only for use by drivers
> that require muxes, and did in particular not consider optional muxes or
> to compile as a module.
>
> Over time several drivers have added a "select MULTIPLEXER" dependency,
> some of which require a mux and some consider it optional. v7.0-rc1
> shows 15 such occurrences in Kconfig files, in a variety of subsystems.
>
> Further some drivers such as gpio-mux are useful on their own (e.g.
> through device-tree idle-state property), but can not currently be
> selected through menuconfig unless another driver selecting MULTIPLEXER
> symbol was enabled first.
>
> The natural step forward to allow enabling mux core and drivers would be
> adding prompt and help text to the existing symbol.
>
> This violates the general kbuild advice to avoid selecting visible
> symbols.
>
> Alternatively addition of a wrapper symbol MUX_CORE was considered,
> which in turn would "select MULTIPLEXER". This however creates new
> issues and confusion as MULTIPLEXER and MUX_CORE need to share the same
> state, i.e. MUX_CORE in menuconfig must not be set to m while
> MULTIPLEXER was selected builtin. Further confusion occurs with Kconfig
> "depends on" relationships that could reference either MUX_CORE or
> MULTIPLEXER.
>
> It is common across the tree for subsystem symbols to be both visible
> and selected, e.g. I2C & SPI. In the same spirit multiplexer needs to
> ignore this particular kbuild rule.
>
> Add prompt and help text to the existing MULTIPLEXER symbol, making it
> visible in (menu)config without breaking existing "select MULTIPLEXER"
> occurrences in the tree.
>
> Select it by default when COMPILE_TEST is set for better coverage.
>
> Signed-off-by: Josua Mayer <josua@xxxxxxxxxxxxx>
> ---
>  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

Allowing the core being a module makes things/code a bit unnecessarily
complicated, I think.

Similar to other subsystems (like regulators/clk/etc), the core is a
bool and the menu below it for its provider drivers depends on it to
be configurable, allowing them to be tristate.

> +       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.
>

continuing from the above comment, this would instead be:

if MULTIPLEXER

menu "Multiplexer drivers"


>  menu "Multiplexer drivers"
>         depends on MULTIPLEXER
>
> --
> 2.43.0
>

Kind regards
Uffe