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

[Wolfram Sang <wsa+renesas@sang-engineering.com>]

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@solid-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@sang-engineering.com>