linux-kernel - Re: [PATCH v3 2/6] mux: Add helper functions for getting optional and selected mux-state

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Message-ID: <CAMuHMdXjAS6HOYy5=uxcK0RZL5X6agRoHG67QUw4xh5+ovZaJQ@mail.gmail.com>
Date: Mon, 22 Dec 2025 11:08:11 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Josua Mayer <josua@...id-run.com>
Cc: 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>, Marc Kleine-Budde <mkl@...gutronix.de>, 
	Vincent Mailhol <mailhol@...nel.org>, Vinod Koul <vkoul@...nel.org>, 
	Kishon Vijay Abraham I <kishon@...nel.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>, Vignesh R <vigneshr@...com>, 
	Janusz Krzysztofik <jmkrzyszt@...il.com>, Andi Shyti <andi.shyti@...nel.org>, 
	Mikhail Anikin <mikhail.anikin@...id-run.com>, Yazan Shhady <yazan.shhady@...id-run.com>, 
	Jon Nettleton <jon@...id-run.com>, linux-mmc@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org, 
	linux-can@...r.kernel.org, linux-phy@...ts.infradead.org, 
	linux-omap@...r.kernel.org, linux-i2c@...r.kernel.org
Subject: Re: [PATCH v3 2/6] mux: Add helper functions for getting optional and
 selected mux-state

Hi Josua,

On Wed, 10 Dec 2025 at 18:39, Josua Mayer <josua@...id-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:
>
> - devm_mux_state_get_optional:
>   Get a mux-state if specified in dt, return NULL 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 return -ENOENT in case dt
> did not specify a mux-state or -control matching given name (if valid).
> This matches of_parse_phandle_with_args semantics which also returns
> -ENOENT if the property does nto exists, or its value is zero.
>
> The new helper functions check for ENOENT to return NULL for optional
> muxes.
>
> 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. This is removed as the returned error code (-ENOENT) is clear.
>
> The second error message is based on of_parse_phandle_with_args return
> value. In case mux description is missing from DT, it returns -ENOENT.
> Print error message only for other error codes.
>
> This ensures that the new helper functions will not confuse the user
> either.
>
> Signed-off-by: Josua Mayer <josua@...id-run.com>

Thanks for your patch!

> --- a/drivers/mux/core.c
> +++ b/drivers/mux/core.c
> @@ -542,11 +542,8 @@ 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) {
> -                       dev_err(dev, "mux controller '%s' not found\n",
> -                               mux_name);
> -                       return ERR_PTR(index);
> -               }
> +               if (index < 0)
> +                       return ERR_PTR(-ENOENT);
>         }
>
>         if (state)
> @@ -558,8 +555,10 @@ static struct mux_control *mux_get(struct device *dev, const char *mux_name,
>                                                  "mux-controls", "#mux-control-cells",
>                                                  index, &args);
>         if (ret) {
> -               dev_err(dev, "%pOF: failed to get mux-%s %s(%i)\n",
> -                       np, state ? "state" : "control", mux_name ?: "", index);
> +               if (ret != -ENOENT)

I think the non-optional variant should still print an error message in
case of -ENOENT, else this has to be duplicated in all drivers using it.

This is typically handled by having a non-printing core helper function,
and having printing non-optional, and non-printing/ignoring optional wrappers
around the former.

> +                       dev_err(dev, "%pOF: failed to get mux-%s %s(%i)\n",
> +                               np, state ? "state" : "control",
> +                               mux_name ?: "", index);
>                 return ERR_PTR(ret);
>         }
>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

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