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

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Message-ID: <20250117092704.2b4a1a1c@bootlin.com>
Date: Fri, 17 Jan 2025 09:27:04 +0100
From: Herve Codina <herve.codina@...tlin.com>
To: Uwe Kleine-König <ukleinek@...nel.org>,
 u.kleine-koenig@...libre.com
Cc: Rob Herring <robh@...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

Hi All,

I haven't receive any feedback on this patch neither the v1 nor this v2.

Maybe an issue with the mail. Add u.kleine-koenig@...libre.com and hope to
have a feedback on this patch.

Best regards,
Hervé

On Wed,  8 Jan 2025 17:18:53 +0100
Herve Codina <herve.codina@...tlin.com> 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().
> 
> Add support for nexus node device-tree binding and the related remapping
> in the PWM subsystem by simply using of_parse_phandle_with_args_map()
> instead of of_parse_phandle_with_args().
> 
> [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>
> ---
> Changes v1 -> v2
>   - Rework commit log
> 
>  drivers/pwm/core.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> index 9c733877e98e..4a7454841cef 100644
> --- a/drivers/pwm/core.c
> +++ b/drivers/pwm/core.c
> @@ -1707,8 +1707,7 @@ static struct pwm_device *of_pwm_get(struct device *dev, struct device_node *np,
>  			return ERR_PTR(index);
>  	}
>  
> -	err = of_parse_phandle_with_args(np, "pwms", "#pwm-cells", index,
> -					 &args);
> +	err = of_parse_phandle_with_args_map(np, "pwms", "pwm", index, &args);
>  	if (err) {
>  		pr_err("%s(): can't parse \"pwms\" property\n", __func__);
>  		return ERR_PTR(err);