linux-kernel - Re: [PATCH v5 1/2] dt-bindings: i2c: pca954x: Add timeout reset property

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Message-ID: <20241018135314.GA91900-robh@kernel.org>
Date: Fri, 18 Oct 2024 08:53:14 -0500
From: Rob Herring <robh@...nel.org>
To: Wojciech Siudy <wojciech.siudy@...ia.com>
Cc: linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
	devicetree@...r.kernel.org, andi.shyti@...nel.org, peda@...ntia.se
Subject: Re: [PATCH v5 1/2] dt-bindings: i2c: pca954x: Add timeout reset
 property

On Fri, Oct 18, 2024 at 12:03:37PM +0200, Wojciech Siudy wrote:
> For cases when the mux shares reset line with other chips we cannot
> use it always when channel selection or deselection times out, because
> it could break them without proper init/probe. The property is
> necessary, because reset lines are board-specific.
> 
> Signed-off-by: Wojciech Siudy <wojciech.siudy@...ia.com>
> 
> ---
> Changelog:
> v5:
>   * Declare dependency of a new property
> ---
>  .../devicetree/bindings/i2c/i2c-mux-pca954x.yaml      | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.yaml b/Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.yaml
> index 9aa0585200c9..37882a5a8c87 100644
> --- a/Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.yaml
> +++ b/Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.yaml
> @@ -63,6 +63,11 @@ properties:
>        necessary for example, if there are several multiplexers on the bus and
>        the devices behind them use same I2C addresses.
>  
> +  i2c-mux-timeout-reset:
> +    type: boolean
> +    description: Sends reset pulse if channel selection or deselection times
> +      out. Do not use if other chips share the same reset line.

If you have a reset GPIO for the mux, then why wouldn't just use it on 
timeout? What happens if you timeout and don't have this property? Just 
give up? 

Does the timeout time need to be configurable?

> +
>    idle-state:
>      description: if present, overrides i2c-mux-idle-disconnect
>      $ref: /schemas/mux/mux-controller.yaml#/properties/idle-state
> @@ -88,6 +93,9 @@ properties:
>        register activates a channel to detect a stuck high fault. On fault the
>        channel is isolated from the upstream bus.
>  
> +dependencies:
> +  i2c-mux-timeout-reset: [ reset-gpios ]
> +
>  required:
>    - compatible
>    - reg
> @@ -146,6 +154,9 @@ examples:
>              interrupt-parent = <&ipic>;
>              interrupts = <17 IRQ_TYPE_LEVEL_LOW>;
>              interrupt-controller;
> +            reset-gpios = <&gpio1 27 1>;
> +            i2c-mux-idle-disconnect;
> +            i2c-mux-timeout-reset;
>              #interrupt-cells = <2>;
>  
>              i2c@2 {
> -- 
> 2.34.1
>