linux-kernel - Re: [PATCH v8 3/7] mux: add help text for MULTIPLEXER config option

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Message-ID: <CAMuHMdWa6o19+oX=-Hkpx+tEsnJ39vyi91FwbU+YHJqv=QsPkA@mail.gmail.com>
Date: Mon, 9 Feb 2026 12:03:34 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Josua Mayer <josua@...id-run.com>
Cc: Marc Kleine-Budde <mkl@...gutronix.de>, Vincent Mailhol <mailhol@...nel.org>, 
	Vinod Koul <vkoul@...nel.org>, Neil Armstrong <neil.armstrong@...aro.org>, 
	Peter Rosin <peda@...ntia.se>, 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>, 
	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 v8 3/7] mux: add help text for MULTIPLEXER config option

Hi Josua,

On Mon, 9 Feb 2026 at 11:47, Josua Mayer <josua@...id-run.com> wrote:
> On 09/02/2026 12:17, Geert Uytterhoeven wrote:
> > On Mon, 9 Feb 2026 at 11:12, Josua Mayer <josua@...id-run.com> wrote:
> >> On 09/02/2026 10:06, Geert Uytterhoeven wrote:
> >>> On Sun, 8 Feb 2026 at 16:16, Josua Mayer <josua@...id-run.com> wrote:
> >>>> On 03/02/2026 15:01, 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 | 8 +++++++-
> >>>>>     1 file changed, 7 insertions(+), 1 deletion(-)
> >>>>>
> >>>>> diff --git a/drivers/mux/Kconfig b/drivers/mux/Kconfig
> >>>>> index c68132e38138..e31c46820bdf 100644
> >>>>> --- a/drivers/mux/Kconfig
> >>>>> +++ b/drivers/mux/Kconfig
> >>>>> @@ -4,7 +4,13 @@
> >>>>>     #
> >>>>>
> >>>>>     config MULTIPLEXER
> >>>>> -     tristate
> >>>>> +     tristate "Generic Multiplexer Support" if COMPILE_TEST
> >>>> This didn't do what I thought it would.
> >>>> It was my intention to allow enabling this through menuconfig / .config.
> >>>>
> >>>> With the syntax above menuconfig shows:
> >>>>
> >>>> │ Symbol: MULTIPLEXER [=n]
> >>>> │ Type  : tristate
> >>>> │ Defined at drivers/mux/Kconfig:6
> >>>> │   Prompt: Generic Multiplexer Support
> >>>> │   Visible if: COMPILE_TEST [=n]
> >>>>
> >>>> This means it cannot be selected.
> >>> Looks like you haven't enabled COMPILE_TEST first?
> >> Correct.
> >> But CONFIG_MULTIPLEXER should be visible always,
> >> not just when COMPILE_TEST is set.
> > Why should it always be visible? All users select it?
>
> This is not relevant for v7 now and can be handled later.
>
> It was discussed previously that drivers supporting optional muxes
> do not need to "select" MULTIPLEXER through Kconfig,
> E.g. the renesas sdhi driver.
>
> However other drivers are already selecting it even though the mux
> is optional, see e.g. phy-can-transceiver.
>
> In order to support muxes in renesas sdhi driver e.g., users must choose to
> enable both the renesas driver, and multiplexer subsystem via the
> configuration.
>
> The mux core standalone also supports a limited use-case without other
> driver
> interactions, setting idle-state e.g.:
>
> mux-controller {
>      compatible = "gpio-mux";
>      #mux-control-cells = <0>;
>      mux-gpios = <&tca6416_u20 0 GPIO_ACTIVE_HIGH>;
>      idle-state = <0>;
> };
>
> So it can be generally useful for a user to enable CONFIG_MULTIPLEXER.

Then please say so in the patch description.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds