linux-kernel - Re: [PATCH v2 1/1] pwm: Add support for pwm nexus dt bindings

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Message-ID: <20250117133854.GA500748-robh@kernel.org>
Date: Fri, 17 Jan 2025 07:38:54 -0600
From: Rob Herring <robh@...nel.org>
To: Herve Codina <herve.codina@...tlin.com>
Cc: Uwe Kleine-König <ukleinek@...nel.org>,
	Saravana Kannan <saravanak@...gle.com>, 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 v2 1/1] pwm: Add support for pwm nexus dt bindings

On Wed, Jan 08, 2025 at 05:18:53PM +0100, Herve Codina wrote:
> Platforms can have a standardized connector/expansion slot that exposes
> signals like PWMs to expansion boards in an SoC agnostic way.
> 
> The support for nexus node [1] has been added to handle those cases in
> commit bd6f2fd5a1d5 ("of: Support parsing phandle argument lists through
> a nexus node"). This commit introduced of_parse_phandle_with_args_map()
> to handle nexus nodes in a generic way and the gpio subsystem adopted
> the support in commit c11e6f0f04db ("gpio: Support gpio nexus dt
> bindings").
> 
> A nexus node allows to remap a phandle list in a consumer node through a
> connector node in a generic way. With this remapping supported, the
> consumer node needs to knwow 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.
> 
> The nexus node remapping handling consists in handling #*-cells, *-map,
> *-map-mask and *-map-pass-thru properties. This is already supported
> by of_parse_phandle_with_args_map().

You need a schema for all these properties (pwm-map, etc.). A wildcard 
doesn't work because '-map$' is not unique:

$ dt-extract-props Documentation/devicetree/bindings/ | grep '\-map'
 'adi,pdm-clk-map': ['uint32-array'],
 'arm,v2m-memory-map': ['string'],
 'brcm,ccode-map': ['string-array'],
 'brcm,ccode-map-trivial': ['flag'],
 'brcm,int-map-mask': ['uint32-array'],
 'charge-current-limit-mapping': ['uint32-matrix'],
 'dai-tdm-slot-width-map': ['uint32-matrix'],
 'data-mapping': ['string-array'],
 'fsl,asrc-clk-map': ['uint32'],
 'gpio-fan,speed-map': ['uint32-matrix'],
 'gpio-map': ['uint32-matrix'],
 'gpio-map-mask': ['uint32-array'],
 'gpio-map-pass-thru': ['uint32-array'],
 'intel,vm-map': ['uint8-array'],
 'interrupt-map': ['uint32-matrix'],
 'interrupt-map-mask': ['uint32-array'],
 'iommu-map': ['uint32-matrix'],
 'iommu-map-mask': ['uint32'],
 'linux,rc-map-name': ['string'],
 'msi-map': ['uint32-matrix'],
 'msi-map-mask': ['uint32'],
 'mstar,irqs-map-range': ['uint32-matrix'],
 'no-map': ['flag'],
 'port-mapping-mode': ['flag'],
 'qcom,mpm-pin-map': ['uint32-matrix'],
 'qcom,port-mapping': ['uint32-array'],
 'qcom,rx-port-mapping': ['uint32-array'],
 'qcom,tx-port-mapping': ['uint32-array'],
 'rockchip,path-map': ['uint32-array'],
 'ti,linear-mapping-mode': ['flag'],

Rob