Subject: Re: [PATCH 2/5] dt-bindings: pinctrl: Add generic pinctrl for board-level mux chips

From: Rob Herring <[email-masked]>
Date: Mon, 23 Feb 2026 12:42:52 -0600

On Thu, Feb 19, 2026 at 05:23:42PM -0500, Frank Li wrote:
> Add a generic pinctrl binding for board-level pinmux chips that are
> controlled through the multiplexer subsystem.
> 
> On some boards, especially development boards, external mux chips are used
> to switch SoC signals between different peripherals (e.g. MMC and UART).
> The mux select lines are often driven by a GPIO expander over I2C,
> as illustrated below:
> 
> 	┌──────┐      ┌─────┐
> 	│ SOC  │      │     │    ┌───────┐
> 	│      │      │     │───►│ MMC   │
> 	│      │      │ MUX │    └───────┘
> 	│      ├─────►│     │    ┌───────┐
> 	│      │      │     │───►│ UART  │
> 	│      │      └─────┘    └───────┘
> 	│      │         ▲
> 	│      │    ┌────┴──────────────┐
> 	│ I2C  ├───►│ GPIO Expander     │
> 	└──────┘    └───────────────────┘
> 
> Traditionally, gpio-hog is used to configure the onboard mux at boot.
> However, the GPIO expander may probe later than consumer devices such as
> MMC. As a result, the MUX might not be configured when the peripheral
> driver probes, leading to initialization failures or data transfer errors.
> 
> Introduce a generic pinctrl binding that models the board-level MUX as a
> pin control provider and builds proper device links between the MUX, its
> GPIO controller, and peripheral devices. This ensures correct probe
> ordering and reliable mux configuration.
> 
> The implementation leverages the standard multiplexer subsystem, which
> provides broad support for onboard mux controllers and avoids the need for
> per-driver custom MUX handling.

Seems reasonable to me.

> 
> Allow pinctrl-* pattern as node name because this pinctrl device have not
> reg property.
> 
> Signed-off-by: Frank Li <[email-masked]>
> ---
>  .../bindings/pinctrl/pinctrl-multiplexer.yaml      | 54 ++++++++++++++++++++++
>  .../devicetree/bindings/pinctrl/pinctrl.yaml       |  2 +-
>  2 files changed, 55 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/devicetree/bindings/pinctrl/pinctrl-multiplexer.yaml b/Documentation/devicetree/bindings/pinctrl/pinctrl-multiplexer.yaml
> new file mode 100644
> index 0000000000000000000000000000000000000000..31efffb3167cba724b1afe0d403a0dcae65582ee
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/pinctrl/pinctrl-multiplexer.yaml
> @@ -0,0 +1,54 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/pinctrl/pinctrl-multiplexer.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Generic Pin Control Driver for Board-Level Mux Chips
> +
> +maintainers:
> +  - Frank Li <[email-masked]>
> +
> +description:
> +  This binding describes a generic pinctrl driver that controls on-board

Bindings don't describe drivers.

> +  pinmux chips using the multiplexer subsystem.
> +
> +properties:
> +  compatible:
> +    const: pinctrl-multiplexer
> +
> +patternProperties:
> +  '-grp$':
> +    type: object

       additionalProperties: false

The tools should have caught this, I'll have to check why not...

> +    properties:
> +      mux-states:
> +        maxItems: 1
> +
> +    required:
> +      - mux-states
> +
> +required:
> +  - compatible
> +
> +allOf:
> +  - $ref: pinctrl.yaml#
> +
> +unevaluatedProperties: false
> +
> +examples:
> +  - |
> +    pinctrl-mux {
> +        compatible = "pinctrl-multiplexer";
> +
> +        uart-grp {
> +            mux-states = <&mux 0>;
> +        };
> +
> +        spi-grp {
> +            mux-states = <&mux 1>;
> +        };
> +
> +        i2c-grp {
> +            mux-states = <&mux 2>;
> +        };
> +    };
> diff --git a/Documentation/devicetree/bindings/pinctrl/pinctrl.yaml b/Documentation/devicetree/bindings/pinctrl/pinctrl.yaml
> index 290438826c507ec6725f486d18cf686aa7c35e67..20176bf3074757de30f208e69b968a6bd6125273 100644
> --- a/Documentation/devicetree/bindings/pinctrl/pinctrl.yaml
> +++ b/Documentation/devicetree/bindings/pinctrl/pinctrl.yaml
> @@ -27,7 +27,7 @@ description: |
>  
>  properties:
>    $nodename:
> -    pattern: "^(pinctrl|pinmux)(@[0-9a-f]+)?$"
> +    pattern: "^(pinctrl|pinmux)(@[0-9a-f]+|-[a-z0-9]+)?$"
>  
>    "#pinctrl-cells":
>      description: >
> 
> -- 
> 2.43.0
>