Re: [PATCH v2] mux: gpio-mux: add support for 4:1 2-channels mux

[Peter Rosin <peda@lysator.liu.se>]

On 2026-05-06 14:33, Andrea Tomassetti wrote:
> Some gpio multiplexers, like TMUX1209, offer differential 4:1
> or dual 4:1 single-ended channels. No binding changes are needed
> because the DT binding already supports #mux-control-cells
> with values 0 and 1. So, similarly to what was 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.
> 
> As an example, 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>;
> 	};
> 
> And use it like this:
> 
> 	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@sipearl.com>
> Reviewed-by: Linus Walleij <linusw@kernel.org>

Hi!

Sorry for the extremely late reply.

This patch is not needed and makes no sense at all. You should be
able to describe the hardware like below instead. I.e., no need for
an extra controller. The mux subsystem handles multiple clients to
the same mux controller as mux controllers are always shared.

	tmux1209: mux-controller {
		compatible = "gpio-mux";
		#mux-control-cells = <0>;

		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>;

		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>;

		channels = "S1B", "S2B", "S3B", "S4B";
	};

An extra controller would have been needed if it was different
gpios for mux A and B. But it's not. You cannot change mux A
without affecting mux B, so the mux controller absolutely must be
shared between A and B.

I hope that helps.

Cheers,
Peter