linux-kernel - Re: [PATCH v3 2/6] mux: Add helper functions for getting optional and selected mux-state

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Message-ID: <CAPDyKFqN1Yq0atE6YaeigzR75n1Q1BSU8JjLno=ioUBwN8=FSQ@mail.gmail.com>
Date: Mon, 29 Dec 2025 15:46:32 +0100
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Josua Mayer <josua@...id-run.com>
Cc: 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>, 
	Marc Kleine-Budde <mkl@...gutronix.de>, Vincent Mailhol <mailhol@...nel.org>, Vinod Koul <vkoul@...nel.org>, 
	Kishon Vijay Abraham I <kishon@...nel.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>, Vignesh R <vigneshr@...com>, 
	Janusz Krzysztofik <jmkrzyszt@...il.com>, Andi Shyti <andi.shyti@...nel.org>, 
	Mikhail Anikin <mikhail.anikin@...id-run.com>, Yazan Shhady <yazan.shhady@...id-run.com>, 
	Jon Nettleton <jon@...id-run.com>, "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>, 
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>, 
	"linux-can@...r.kernel.org" <linux-can@...r.kernel.org>, 
	"linux-phy@...ts.infradead.org" <linux-phy@...ts.infradead.org>, 
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>, 
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>
Subject: Re: [PATCH v3 2/6] mux: Add helper functions for getting optional and
 selected mux-state

On Mon, 29 Dec 2025 at 12:30, Josua Mayer <josua@...id-run.com> wrote:
>
> Am 22.12.25 um 15:47 schrieb Ulf Hansson:
> > On Sun, 21 Dec 2025 at 11:38, Josua Mayer <josua@...id-run.com> wrote:
> >> Hi Ulf,
> >>
> >> Am 17.12.25 um 14:38 schrieb Ulf Hansson:
> >>> On Wed, 10 Dec 2025 at 18:39, Josua Mayer <josua@...id-run.com> wrote:
> >> cut
> >>
> >>>>  /*
> >>>>   * Using subsys_initcall instead of module_init here to try to ensure - for
> >>>>   * the non-modular case - that the subsystem is initialized when mux consumers
> >>>> diff --git a/include/linux/mux/consumer.h b/include/linux/mux/consumer.h
> >>>> index 2e25c838f8312..a5da2e33a45c0 100644
> >>>> --- a/include/linux/mux/consumer.h
> >>>> +++ b/include/linux/mux/consumer.h
> >>>> @@ -60,5 +60,9 @@ struct mux_control *devm_mux_control_get(struct device *dev,
> >>>>                                          const char *mux_name);
> >>>>  struct mux_state *devm_mux_state_get(struct device *dev,
> >>>>                                      const char *mux_name);
> >>>> +struct mux_state *devm_mux_state_get_optional(struct device *dev,
> >>>> +                                             const char *mux_name);
> >>>> +struct mux_state *devm_mux_state_get_optional_selected(struct device *dev,
> >>>> +                                                      const char *mux_name);
> >>> Seems like we need stub-functions of these too. Otherwise
> >>> subsystems/drivers need to have a "depends on MULTIPLEXER" in their
> >>> Kconfigs.
> >> Currently the drivers that can use a mux select MULTIPLEXER in Kconfig.
> > Yes, but that's not generally how we do this. The driver may not need
> > MULTIPLEXER for all platforms that driver is being used on.
> >
> >> There already exist a few mux helpers both for mux-state and for mux-control,
> >> and they might all need stubs.
> > Correct. I think we should add subs for all of them.
> >
> >> I'd prefer the restructuring of kconfig dependencies being independent from
> >> adding mux-state functionality to renesas sdhi driver.
> > I understand your point, but adding the stubs isn't really a big thing
> > - unless someone has some good arguments not to!?
> >
> > Moreover, since the series changes the mux-core anyways - and
> > subsequent changes depend on it, I don't see an issue to fold in yet
> > another patch to add the stubs.
> Would this also cause changing all the Kconfig "select MULTIPLEXER"?
> If it is only the stubs - sure.
>
> And then in the renesas sdhi patch I can drop my change to kconfig.

Correct!

Typically, it's better to do a "select MULTIPLEXER" in the platform's
Kconfig for those platforms that really need it.

Kind regards
Uffe