linux-kernel - Re: [PATCH v4 1/6] dt-bindings: pwm: amlogic: fix s4 bindings

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Date: Wed, 17 Jan 2024 11:03:16 +0100
From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To: Jerome Brunet <jbrunet@...libre.com>
Cc: Thierry Reding <thierry.reding@...il.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	Kevin Hilman <khilman@...libre.com>, devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-amlogic@...ts.infradead.org, linux-pwm@...r.kernel.org, JunYi Zhao <junyi.zhao@...ogic.com>, 
	Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v4 1/6] dt-bindings: pwm: amlogic: fix s4 bindings

On Fri, Dec 22, 2023 at 12:16:49PM +0100, Jerome Brunet wrote:
> s4 has been added to the compatible list while converting the Amlogic PWM
> binding documentation from txt to yaml.
> 
> However, on the s4, the clock bindings have different meaning compared to
> the previous SoCs.
> 
> On the previous SoCs the clock bindings used to describe which input the
> PWM channel multiplexer should pick among its possible parents.
> 
> This is very much tied to the driver implementation, instead of describing
> the HW for what it is. When support for the Amlogic PWM was first added,
> how to deal with clocks through DT was not as clear as it nowadays.
> The Linux driver now ignores this DT setting, but still relies on the
> hard-coded list of clock sources.
> 
> On the s4, the input multiplexer is gone. The clock bindings actually
> describe the clock as it exists, not a setting. The property has a
> different meaning, even if it is still 2 clocks and it would pass the check
> when support is actually added.
> 
> Also the s4 cannot work if the clocks are not provided, so the property no
> longer optional.

s/no/is no/

> Finally, for once it makes sense to see the input as being numbered
> somehow. No need to bother with clock-names on the s4 type of PWM.
> 
> Fixes: 43a1c4ff3977 ("dt-bindings: pwm: Convert Amlogic Meson PWM binding")
> Reviewed-by: Rob Herring <robh@...nel.org>
> Signed-off-by: Jerome Brunet <jbrunet@...libre.com>
> ---
>  .../devicetree/bindings/pwm/pwm-amlogic.yaml  | 67 ++++++++++++++++---
>  1 file changed, 58 insertions(+), 9 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/pwm/pwm-amlogic.yaml b/Documentation/devicetree/bindings/pwm/pwm-amlogic.yaml
> index 527864a4d855..a1d382aacb82 100644
> --- a/Documentation/devicetree/bindings/pwm/pwm-amlogic.yaml
> +++ b/Documentation/devicetree/bindings/pwm/pwm-amlogic.yaml
> @@ -9,9 +9,6 @@ title: Amlogic PWM
>  maintainers:
>    - Heiner Kallweit <hkallweit1@...il.com>
>  
> -allOf:
> -  - $ref: pwm.yaml#
> -
>  properties:
>    compatible:
>      oneOf:
> @@ -43,12 +40,8 @@ properties:
>      maxItems: 2
>  
>    clock-names:
> -    oneOf:
> -      - items:
> -          - enum: [clkin0, clkin1]
> -      - items:
> -          - const: clkin0
> -          - const: clkin1
> +    minItems: 1
> +    maxItems: 2
>  
>    "#pwm-cells":
>      const: 3
> @@ -57,6 +50,55 @@ required:
>    - compatible
>    - reg
>  
> +allOf:
> +  - $ref: pwm.yaml#
> +
> +  - if:
> +      properties:
> +        compatible:
> +          contains:
> +            enum:
> +              - amlogic,meson8-pwm
> +              - amlogic,meson8b-pwm
> +              - amlogic,meson-gxbb-pwm
> +              - amlogic,meson-gxbb-ao-pwm
> +              - amlogic,meson-axg-ee-pwm
> +              - amlogic,meson-axg-ao-pwm
> +              - amlogic,meson-g12a-ee-pwm
> +              - amlogic,meson-g12a-ao-pwm-ab
> +              - amlogic,meson-g12a-ao-pwm-cd
> +    then:
> +      # Historic bindings tied to the driver implementation
> +      # The clocks provided here are meant to be matched with the input
> +      # known (hard-coded) in the driver and used to select pwm clock
> +      # source. Currently, the linux driver ignores this.

I admit I didn't understand the relevant difference between the old and
the new binding yet. (The driver currently doesn't support the s4,
right?) Is it possible to detect if the dt uses the old or the new
binding? If yes, I suggest to drop the old one from the binding and only
keep it in the driver for legacy systems.

> +      properties:
> +        clock-names:
> +          oneOf:
> +            - items:
> +                - enum: [clkin0, clkin1]
> +            - items:
> +                - const: clkin0
> +                - const: clkin1
> +
> +  # Newer IP block take a single input per channel, instead of 4 inputs
> +  # for both channels
> +  - if:
> +      properties:
> +        compatible:
> +          contains:
> +            enum:
> +              - amlogic,meson-s4-pwm

The expectation is that this list contains all compatibles that are not
included in the "historic" list above, right? Then maybe use "else:"
instead of another explicit list?

> +    then:
> +      properties:
> +        clocks:
> +          items:
> +            - description: input clock of PWM channel A
> +            - description: input clock of PWM channel B
> +        clock-names: false
> +      required:
> +        - clocks
> +
>  additionalProperties: false

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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