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Message-ID: <e6bccab9-79ce-4b9b-942e-01c504228d7b@solid-run.com>
Date: Tue, 3 Feb 2026 15:35:37 +0000
From: Josua Mayer <josua@...id-run.com>
To: 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>
CC: 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>, Dan
Carpenter <dan.carpenter@...aro.org>
Subject: Re: [PATCH v8 2/7] mux: Add helper functions for getting optional and
selected mux-state
On 03/02/2026 15:01, 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>
> ---
> drivers/mux/core.c | 205 ++++++++++++++++++++++++++++++++++++-------
> include/linux/mux/consumer.h | 108 ++++++++++++++++++++++-
> 2 files changed, 278 insertions(+), 35 deletions(-)
>
> diff --git a/drivers/mux/core.c b/drivers/mux/core.c
> index a3840fe0995f..2e8295e3aabe 100644
> --- a/drivers/mux/core.c
> +++ b/drivers/mux/core.c
> @@ -46,6 +46,16 @@ static const struct class mux_class = {
> .name = "mux",
> };
>
> +/**
> + * struct devm_mux_state_state - Tracks managed resources for mux-state objects.
> + * @mstate: Pointer to a mux state.
> + * @exit: An optional callback to execute before free.
> + */
> +struct devm_mux_state_state {
> + struct mux_state *mstate;
> + int (*exit)(struct mux_state *mstate);
> +};
> +
> static DEFINE_IDA(mux_ida);
>
> static int __init mux_init(void)
> @@ -516,17 +526,19 @@ static struct mux_chip *of_find_mux_chip_by_node(struct device_node *np)
> return dev ? to_mux_chip(dev) : NULL;
> }
>
> -/*
> +/**
> * mux_get() - Get the mux-control for a device.
> * @dev: The device that needs a mux-control.
> * @mux_name: The name identifying the mux-control.
> * @state: Pointer to where the requested state is returned, or NULL when
> * the required multiplexer states are handled by other means.
> + * @optional: Whether to return NULL and silence errors when mux doesn't exist.
> *
> - * Return: A pointer to the mux-control, or an ERR_PTR with a negative errno.
> + * Return: Pointer to the mux-control on success, an ERR_PTR with a negative errno on error,
> + * or NULL if optional is true and mux doesn't exist.
> */
> static struct mux_control *mux_get(struct device *dev, const char *mux_name,
> - unsigned int *state)
> + unsigned int *state, bool optional)
> {
> struct device_node *np = dev->of_node;
> struct of_phandle_args args;
> @@ -542,7 +554,9 @@ static struct mux_control *mux_get(struct device *dev, const char *mux_name,
> else
> index = of_property_match_string(np, "mux-control-names",
> mux_name);
> - if (index < 0) {
> + if (index < 0 && optional) {
> + return NULL;
> + } else if (index < 0) {
> dev_err(dev, "mux controller '%s' not found\n",
> mux_name);
> return ERR_PTR(index);
> @@ -558,8 +572,12 @@ static struct mux_control *mux_get(struct device *dev, const char *mux_name,
> "mux-controls", "#mux-control-cells",
> index, &args);
> if (ret) {
> + if (optional && ret == -ENOENT)
> + return NULL;
> +
> dev_err(dev, "%pOF: failed to get mux-%s %s(%i)\n",
> - np, state ? "state" : "control", mux_name ?: "", index);
> + np, state ? "state" : "control",
> + mux_name ?: "", index);
> return ERR_PTR(ret);
> }
>
> @@ -617,10 +635,28 @@ static struct mux_control *mux_get(struct device *dev, const char *mux_name,
> */
> struct mux_control *mux_control_get(struct device *dev, const char *mux_name)
> {
> - return mux_get(dev, mux_name, NULL);
> + struct mux_control *mux = mux_get(dev, mux_name, NULL, false);
> +
> + if (!mux)
> + return ERR_PTR(-ENOENT);
> +
> + return mux;
> }
> EXPORT_SYMBOL_GPL(mux_control_get);
>
> +/**
> + * mux_control_get_optional() - Get the optional mux-control for a device.
> + * @dev: The device that needs a mux-control.
> + * @mux_name: The name identifying the mux-control.
> + *
> + * Return: A pointer to the mux-control, an ERR_PTR with a negative errno.
* Return: Pointer to the mux-state on success, an ERR_PTR with a
negative errno on error,
* or NULL if mux doesn't exist.
If there will be v9, I shall change this to be more precise similar to
other functions.
> + */
> +struct mux_control *mux_control_get_optional(struct device *dev, const char *mux_name)
> +{
> + return mux_get(dev, mux_name, NULL, true);
> +}
> +EXPORT_SYMBOL_GPL(mux_control_get_optional);
> +
> /**
> * mux_control_put() - Put away the mux-control for good.
> * @mux: The mux-control to put away.
> @@ -657,10 +693,13 @@ struct mux_control *devm_mux_control_get(struct device *dev,
> if (!ptr)
> return ERR_PTR(-ENOMEM);
>
> - mux = mux_control_get(dev, mux_name);
> + mux = mux_get(dev, mux_name, NULL, false);
> if (IS_ERR(mux)) {
> devres_free(ptr);
> return mux;
> + } else if (!mux) {
> + devres_free(ptr);
> + return ERR_PTR(-ENOENT);
> }
>
> *ptr = mux;
> @@ -670,14 +709,16 @@ struct mux_control *devm_mux_control_get(struct device *dev,
> }
> EXPORT_SYMBOL_GPL(devm_mux_control_get);
>
> -/*
> +/**
> * mux_state_get() - Get the mux-state for a device.
> * @dev: The device that needs a mux-state.
> * @mux_name: The name identifying the mux-state.
> + * @optional: Whether to return NULL and silence errors when mux doesn't exist.
> *
> - * Return: A pointer to the mux-state, or an ERR_PTR with a negative errno.
> + * Return: Pointer to the mux-state on success, an ERR_PTR with a negative errno on error,
> + * or NULL if optional is true and mux doesn't exist.
> */
> -static struct mux_state *mux_state_get(struct device *dev, const char *mux_name)
> +static struct mux_state *mux_state_get(struct device *dev, const char *mux_name, bool optional)
> {
> struct mux_state *mstate;
>
...
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