linux-kernel - Re: [PATCH v8 2/7] mux: Add helper functions for getting optional and selected mux-state

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Message-ID: <aYNjdKul53HalKdw@shikoro>
Date: Wed, 4 Feb 2026 16:19:16 +0100
From: Wolfram Sang <wsa+renesas@...g-engineering.com>
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>,
	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-phy@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
	linux-i2c@...r.kernel.org, linux-mmc@...r.kernel.org,
	devicetree@...r.kernel.org, linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH v8 2/7] mux: Add helper functions for getting optional
 and selected mux-state

On Tue, Feb 03, 2026 at 03:01:35PM +0200, Josua Mayer wrote:
> In-tree phy-can-transceiver driver has already implemented a local
> version of devm_mux_state_get_optional.
> 
> The omap-i2c driver gets and selects an optional mux in its probe
> function without using any helper.
> 
> Add new helper functions covering both aforementioned use-cases:
> 
> - mux_control_get_optional:
>   Get a mux-control if specified in dt, return NULL otherwise.
> - devm_mux_state_get_optional:
>   Get a mux-state if specified in dt, return NULL otherwise.
> - devm_mux_state_get_selected:
>   Get and select a mux-state specified in dt, return error otherwise.
> - devm_mux_state_get_optional_selected:
>   Get and select a mux-state if specified in dt, return error or NULL.
> 
> Existing mux_get helper function is changed to take an extra argument
> indicating whether the mux is optional.
> In this case no error is printed, and NULL returned in case of ENOENT.
> 
> Calling code is adapted to handle NULL return case, and to pass optional
> argument as required.
> 
> To support automatic deselect for _selected helper, a new structure is
> created storing an exit pointer similar to clock core which is called on
> release.
> 
> To facilitate code sharing between optional/mandatory/selected helpers,
> a new internal helper function is added to handle quiet (optional) and
> verbose (mandatory) errors, as well as storing the correct callback for
> devm release: __devm_mux_state_get
> 
> Due to this structure devm_mux_state_get_*_selected can no longer print
> a useful error message when select fails. Instead callers should print
> errors where needed.
> 
> Commit e153fdea9db04 ("phy: can-transceiver: Re-instate "mux-states"
> property presence check") noted that "mux_get() always prints an error
> message in case of an error, including when the property is not present,
> confusing the user."
> 
> The first error message covers the case that a mux name is not matched
> in dt. The second error message is based on of_parse_phandle_with_args
> return value.
> 
> In optional case no error is printed and NULL is returned.
> This ensures that the new helper functions will not confuse the user
> either.
> 
> With the addition of optional helper functions it became clear that
> drivers should compile and link even if CONFIG_MULTIPLEXER was not enabled.
> Add stubs for all symbols exported by mux core.
> 
> Signed-off-by: Josua Mayer <josua@...id-run.com>

I trust you guys with this one. I think the interfaces are useful,
though, so maybe like this?

Acked-by: Wolfram Sang <wsa+renesas@...g-engineering.com>