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@xxxxxxxxxxx>
> ---
> .../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@xxxxxxxxxx>
