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

[Geert Uytterhoeven]

On Thu, 29 Jan 2026 at 17:06, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
> On Wed, 28 Jan 2026 at 15:46, Josua Mayer <josua@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> > ---
> >  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@xxxxxxxxx

>
> > +               goto err_mux_state_get;
> >         }

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds