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

[Josua Mayer <josua@solid-run.com>]

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@solid-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;
>   
...