linux-kernel - Re: [PATCH RFC v3 1/4] dt-bindings: mux: Increase the number of arguments in mux-controls

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Date:   Thu, 25 Nov 2021 14:35:38 +0100
From:   Peter Rosin <peda@...ntia.se>
To:     Aswath Govindraju <a-govindraju@...com>
Cc:     Vignesh Raghavendra <vigneshr@...com>, Nishanth Menon <nm@...com>,
        Rob Herring <robh+dt@...nel.org>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-can@...r.kernel.org,
        linux-phy@...ts.infradead.org
Subject: Re: [PATCH RFC v3 1/4] dt-bindings: mux: Increase the number of
 arguments in mux-controls

Hi!

You need to have some description on how #mux-control-cells now work.
The previous description is in mux-consumer.yaml and an update there
is needed.

However, I have realized that the adg792a binding uses #mux-control-cells
to indicate if it should expose its three muxes with one mux-control
and operate the muxes in parallel, or if it should be expose three
independent mux-controls. So, the approach in this series to always
have the #mux-control-cells property fixed at <2> when indicating a
state will not work for that binding. And I see no fix for that binding
without adding a new property.

So, I would like a different approach. Since I dislike how mux-controls
-after this series- is not (always) specifying a mux-control like the name
says, but instead optionally a specific state, the new property I would
like to add is #mux-state-cells such that it would always be one more
than #mux-control-cells.

	mux: mux-controller {
		compatible = "gpio-mux";
		#mux-control-cells = <0>;
		#mux-state-cells = <1>;

		mux-gpios = <...>;
	};

	can-phy {
		compatible = "ti,tcan1043";
		...
		mux-states = <&mux 1>;
	};

That solves the naming issue, the unused argument for mux-conrtrollers
that previously had #mux-control-cells = <0>, and the binding for adg792a
need no longer be inconsistent.

Or, how should this be solved? I'm sure there are other options...

Cheers,
Peter

On 2021-11-23 09:12, Aswath Govindraju wrote:
> Increase the allowed number of arguments in mux-controls to add support for
> passing information regarding the state of the mux to be set, for a given
> device.
> 
> Signed-off-by: Aswath Govindraju <a-govindraju@...com>
> ---
>  Documentation/devicetree/bindings/mux/gpio-mux.yaml       | 2 +-
>  Documentation/devicetree/bindings/mux/mux-controller.yaml | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/mux/gpio-mux.yaml b/Documentation/devicetree/bindings/mux/gpio-mux.yaml
> index 0a7c8d64981a..c810b7df39de 100644
> --- a/Documentation/devicetree/bindings/mux/gpio-mux.yaml
> +++ b/Documentation/devicetree/bindings/mux/gpio-mux.yaml
> @@ -26,7 +26,7 @@ properties:
>        List of gpios used to control the multiplexer, least significant bit first.
>  
>    '#mux-control-cells':
> -    const: 0
> +    enum: [ 0, 1, 2 ]
>  
>    idle-state:
>      default: -1
> diff --git a/Documentation/devicetree/bindings/mux/mux-controller.yaml b/Documentation/devicetree/bindings/mux/mux-controller.yaml
> index 736a84c3b6a5..0b4b067a97bf 100644
> --- a/Documentation/devicetree/bindings/mux/mux-controller.yaml
> +++ b/Documentation/devicetree/bindings/mux/mux-controller.yaml
> @@ -73,7 +73,7 @@ properties:
>      pattern: '^mux-controller(@.*|-[0-9a-f]+)?$'
>  
>    '#mux-control-cells':
> -    enum: [ 0, 1 ]
> +    enum: [ 0, 1, 2 ]
>  
>    idle-state:
>      $ref: /schemas/types.yaml#/definitions/int32
>