Re: [PATCH v7 2/7] mux: Add helper functions for getting optional and selected mux-state

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

On 29/01/2026 18:13, Geert Uytterhoeven wrote:
> On Thu, 29 Jan 2026 at 17:06, Ulf Hansson <ulf.hansson@linaro.org> wrote:
>> On Wed, 28 Jan 2026 at 15:46, Josua Mayer <josua@solid-run.com> 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           | 178 ++++++++++++++++++++++++++++++++++++-------
>>>   include/linux/mux/consumer.h | 108 +++++++++++++++++++++++++-
>>>   2 files changed, 253 insertions(+), 33 deletions(-)
>>>
>>> diff --git a/drivers/mux/core.c b/drivers/mux/core.c
>>> index a3840fe0995f..b01ec126caaf 100644
>>> --- a/drivers/mux/core.c
>>> +++ b/drivers/mux/core.c
>> [...]
>>
>>>   static void devm_mux_state_release(struct device *dev, void *res)
>>>   {
>>> -       struct mux_state *mstate = *(struct mux_state **)res;
>>> +       struct devm_mux_state_state *devm_state = res;
>>>
>>> -       mux_state_put(mstate);
>>> +       if (devm_state->exit)
>>> +               devm_state->exit(devm_state->mstate);
>>> +
>>> +       mux_state_put(devm_state->mstate);
>>>   }
>>>
>>>   /**
>>> - * devm_mux_state_get() - Get the mux-state for a device, with resource
>>> - *                       management.
>>> - * @dev: The device that needs a mux-control.
>>> - * @mux_name: The name identifying the mux-control.
>>> + * __devm_mux_state_get() - Get the optional mux-state for a device,
>>> + *                         with resource management.
>>> + * @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.
>>> + * @init: Optional function pointer for mux-state object initialisation.
>>> + * @exit: Optional function pointer for mux-state object cleanup on release.
>>>    *
>>>    * Return: Pointer to the mux-state, or an ERR_PTR with a negative errno.
>>>    */
>>> -struct mux_state *devm_mux_state_get(struct device *dev,
>>> -                                    const char *mux_name)
>>> +static struct mux_state *__devm_mux_state_get(struct device *dev, const char *mux_name,
>>> +                                             bool optional,
>>> +                                             int (*init)(struct mux_state *mstate),
>>> +                                             int (*exit)(struct mux_state *mstate))
>>>   {
>>> -       struct mux_state **ptr, *mstate;
>>> +       struct devm_mux_state_state *devm_state;
>>> +       struct mux_state *mstate;
>>> +       int ret;
>>>
>>> -       ptr = devres_alloc(devm_mux_state_release, sizeof(*ptr), GFP_KERNEL);
>>> -       if (!ptr)
>>> +       devm_state = devres_alloc(devm_mux_state_release, sizeof(*devm_state), GFP_KERNEL);
>>> +       if (!devm_state)
>>>                  return ERR_PTR(-ENOMEM);
>>>
>>> -       mstate = mux_state_get(dev, mux_name);
>>> -       if (IS_ERR(mstate)) {
>>> -               devres_free(ptr);
>>> -               return mstate;
>>> +       mstate = mux_state_get(dev, mux_name, optional);
>>> +       if (IS_ERR_OR_NULL(mstate)) {
>>> +               ret = PTR_ERR(mstate);
>> Should this be PTR_ERR_OR_ZERO?
> "mux_state_get() never returns NULL"
> https://lore.kernel.org/202601221036.J0kR78Uw-lkp@intel.com

mux_state_get after my modifications does return NULL:

     if (mux_name) {
         ...
         if (index < 0 && optional) {
             return NULL;
         ...
     }
...
     if (ret) {
         if (optional && ret == -ENOENT)
             return NULL;
...

>
>>> +               goto err_mux_state_get;
>>>          }
> Gr{oetje,eeting}s,
>
>                          Geert
>