Re: [PATCH RESEND] mux: gpio-mux: add support for 4:1 2-channels mux

[Linus Walleij]

Hi Andrea,

thanks for your patch!

On Thu, Apr 30, 2026 at 4:13 PM Andrea Tomassetti
<andrea.tomassetti@xxxxxxxxxxx> wrote:

> Some gpio multiplexers, like TMUX1209, offer differential 4:1
> or dual 4:1 single-ended channels. Similarly to what already done by
> the adg792a driver, the gpio-mux driver has to take into account
> the #mux-control-cells property and allocate as many controllers
> as advised by it.
>
> So, in the DTS you can now define:
>
>         tmux1209: mux-controller {
>                 compatible = "gpio-mux";
>                 #mux-control-cells = <1>;
>
>                 mux-gpios = <&gpio_expander 01 GPIO_ACTIVE_HIGH>,
>                                         <&gpio_expander 02 GPIO_ACTIVE_HIGH>;
>         };
>
>         adcmux30: adcmux30 {
>                 compatible = "io-channel-mux";
>                 io-channels = <&adc1 4>;
>                 io-channel-names = "parent";
>                 #io-channel-cells = <1>;
>                 mux-controls = <&tmux1209 0>;
>
>                 channels = "S1A", "S2A", "S3A", "S4A";
>         };
>
>         adcmux31: adcmux31 {
>                 compatible = "io-channel-mux";
>                 io-channels = <&adc1 5>;
>                 io-channel-names = "parent";
>                 #io-channel-cells = <1>;
>                 mux-controls = <&tmux1209 1>;
>
>                 channels = "S1B", "S2B", "S3B", "S4B";
>         };
>
> Signed-off-by: Andrea Tomassetti <andrea.tomassetti@xxxxxxxxxxx>

The mux controller binding looks like this:

properties:
  '#mux-control-cells':
    enum: [ 0, 1 ]

So you do not patch the bindings, you actually implement this
for the case when #mux-control-cells is 1.

Please detail this in the commit.

> -       mux_chip = devm_mux_chip_alloc(dev, 1, sizeof(*mux_gpio));
> +       ret = device_property_read_u32(dev, "#mux-control-cells", &cells);
> +       if (ret < 0)
> +               cells = 0;
> +
> +       if (cells >= 2) {
> +               dev_err(dev, "invalid control-cells %u\n", cells);
> +               return -EINVAL;
> +       }

Maybe put in a comment that the bindings only allow 0 or 1 cell.

> +
> +       mux_chip = devm_mux_chip_alloc(dev, cells + 1, sizeof(*mux_gpio));

Otherwise looks correct to me.

> -       mux_chip->mux->states = BIT(pins);
> +
> +       for (i = 0; i < mux_chip->controllers; ++i)
> +               mux_chip->mux[i].states = BIT(pins);

Is the mux core handling any other specifics? (I guess so...)

With the above added comments, details:
Reviewed-by: Linus Walleij <linusw@xxxxxxxxxx>

Thanks!
Linus Walleij