linux-kernel - Re: [PATCH 2/3] dt-bindings: pwm: adi,axi-pwmgen: add external clock

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Message-ID: <20250521-tidy-heron-of-genius-4dc9a1@kuoka>
Date: Wed, 21 May 2025 12:09:02 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: David Lechner <dlechner@...libre.com>
Cc: Michael Hennerich <michael.hennerich@...log.com>, 
	Nuno Sá <nuno.sa@...log.com>, Trevor Gamblin <tgamblin@...libre.com>, 
	Uwe Kleine-König <ukleinek@...nel.org>, Rob Herring <robh@...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
Subject: Re: [PATCH 2/3] dt-bindings: pwm: adi,axi-pwmgen: add external clock

On Tue, May 20, 2025 at 04:00:45PM GMT, David Lechner wrote:
> Add external clock to the schema.
> 
> The AXI PWMGEN IP block has a compile option ASYNC_CLK_EN that allows
> the use of an external clock for the PWM output separate from the AXI
> clock that runs the peripheral.
> 
> In these cases, we should specify both clocks in the device tree. The
> intention here is that if you specify both clocks, then you include the
> clock-names property and if you don't have an external clock, then you
> omit the clock-names property.
> 
> There can't be more than one allOf: in the top level of the schema, so
> it is stolen from $ref since it isn't needed there and used for the
> more typical case of the if statement (even though technically it isn't
> needed there either at this time).
> 
> Signed-off-by: David Lechner <dlechner@...libre.com>
> ---
>  .../devicetree/bindings/pwm/adi,axi-pwmgen.yaml    | 26 ++++++++++++++++++----
>  1 file changed, 22 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/pwm/adi,axi-pwmgen.yaml b/Documentation/devicetree/bindings/pwm/adi,axi-pwmgen.yaml
> index bc44381692054f647a160a6573dae4cff2ee3f31..90f702a5cd80bd7d62e2436b2eed44314ab4fd53 100644
> --- a/Documentation/devicetree/bindings/pwm/adi,axi-pwmgen.yaml
> +++ b/Documentation/devicetree/bindings/pwm/adi,axi-pwmgen.yaml
> @@ -16,8 +16,7 @@ description:
>  
>    https://analogdevicesinc.github.io/hdl/library/axi_pwm_gen/index.html
>  
> -allOf:
> -  - $ref: pwm.yaml#
> +$ref: pwm.yaml#
>  
>  properties:
>    compatible:
> @@ -30,7 +29,13 @@ properties:
>      const: 3
>  
>    clocks:
> -    maxItems: 1
> +    minItems: 1
> +    maxItems: 2
> +
> +  clock-names:
> +    items:
> +      - const: axi
> +      - const: ext
>  
>  required:
>    - reg
> @@ -38,11 +43,24 @@ required:
>  
>  unevaluatedProperties: false
>  
> +allOf:
> +  - if:
> +      required: [clock-names]


No, don't do that. If you want clock-names, just add them for both
cases. Otherwise, just describe items in clocks and no need for
clock-names.



> +    then:
> +      properties:
> +        clocks:
> +          minItems: 2
> +    else:
> +      properties:
> +        clocks:
> +          maxItems: 1
> +
>  examples:
>    - |
>      pwm@...00000 {
>          compatible = "adi,axi-pwmgen-2.00.a";
>          reg = <0x44b00000 0x1000>;
> -        clocks = <&spi_clk>;
> +        clocks = <&fpga_clk>, <&spi_clk>;

What was the clock[0] before? Axi, right, so SPI_CLK. Now FPGA is the
AXI_CLK? This feels like clock order reversed.

Best regards,
Krzysztof