linux-kernel - Re: [PATCH v3 1/2] dt-bindings: pwm: Add support for PWM nexus node

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Message-ID: <20250211205609.GA1142491-robh@kernel.org>
Date: Tue, 11 Feb 2025 14:56:09 -0600
From: Rob Herring <robh@...nel.org>
To: Herve Codina <herve.codina@...tlin.com>
Cc: Uwe Kleine-König <ukleinek@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, linux-pwm@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	Luca Ceresoli <luca.ceresoli@...tlin.com>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v3 1/2] dt-bindings: pwm: Add support for PWM nexus node

On Wed, Feb 05, 2025 at 10:55:42AM +0100, Herve Codina wrote:
> Platforms can have a standardized connector/expansion slot that exposes
> PWMs signals to expansion boards.
> 
> A nexus node [1] allows to remap a phandle list in a consumer node
> through a connector node in a generic way. With this remapping, the
> consumer node needs to know only about the nexus node. Resources behind
> the nexus node are decoupled by the nexus node itself.
> 
> This is particularly useful when this consumer is described in a
> device-tree overlay. Indeed, to have the exact same overlay reused with
> several base systems the overlay needs to known only about the connector
> is going to be applied to without any knowledge of the SoC (or the
> component providing the resource) available in the system.
> 
> As an example, suppose 3 PWMs connected to a connector. The connector
> PWM 0 and 2 comes from the PWM 1 and 3 of the pwm-controller1. The
> connector PWM 1 comes from the PWM 4 of the pwm-controller2. An
> expansion device is connected to the connector and uses the connector
> PMW 1.
> 
> Nexus node support in PWM allows the following description:
>         soc {
>                 soc_pwm1: pwm-controller1 {
>                         #pwm-cells = <3>;
>                 };
> 
>                 soc_pwm2: pwm-controller2 {
>                         #pwm-cells = <3>;
>                 };
>         };
> 
>         connector: connector {
>                 #pwm-cells = <3>;
>                 pwm-map = <0 0 0 &soc_pwm1 1 0 0>,
>                           <1 0 0 &soc_pwm2 4 0 0>,
>                           <2 0 0 &soc_pwm1 3 0 0>;
>                 pwm-map-mask = <0xffffffff 0x0 0x0>;
>                 pwm-map-pass-thru = <0x0 0xffffffff 0xffffffff>;
>         };
> 
>         expansion_device {
>                 pwms = <&connector 1 57000 0>;
>         };
> 
> >From the expansion device point of view, the PWM requested is the PWM 1
> available at the connector regardless of the exact PWM wired to this
> connector PWM 1. Thanks to nexus node remapping described at connector
> node, this PWM is the PWM 4 of the pwm-controller2.
> 
> [1] https://github.com/devicetree-org/devicetree-specification/blob/v0.4/source/chapter2-devicetree-basics.rst#nexus-nodes-and-specifier-mapping
> 
> Signed-off-by: Herve Codina <herve.codina@...tlin.com>
> ---
>  .../bindings/pwm/pwm-nexus-node.yaml          | 65 +++++++++++++++++++
>  1 file changed, 65 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/pwm/pwm-nexus-node.yaml
> 
> diff --git a/Documentation/devicetree/bindings/pwm/pwm-nexus-node.yaml b/Documentation/devicetree/bindings/pwm/pwm-nexus-node.yaml
> new file mode 100644
> index 000000000000..55412fe50d01
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/pwm/pwm-nexus-node.yaml
> @@ -0,0 +1,65 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/pwm/pwm-nexus-node.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: PWM Nexus node properties
> +
> +description:

You need '>' on the end to preserve paragraphs. With that,

Reviewed-by: Rob Herring (Arm) <robh@...nel.org>