Re: [PATCH v12 1/3] dt-bindings: pwm: Add binding for Allwinner D1/T113-S3/R329 PWM controller

[Andre Przywara <andre.przywara@arm.com>]

On Sun, 27 Apr 2025 17:24:53 +0300
Aleksandr Shubin <privatesub2@gmail.com> wrote:

Hi,

> Allwinner's D1, T113-S3 and R329 SoCs have a new pwm
> controller witch is different from the previous pwm-sun4i.
> 
> The D1 and T113 are identical in terms of peripherals,
> they differ only in the architecture of the CPU core, and
> even share the majority of their DT. Because of that,
> using the same compatible makes sense.
> The R329 is a different SoC though, and should have
> a different compatible string added, especially as there
> is a difference in the number of channels.
> 
> D1 and T113s SoCs have one PWM controller with 8 channels.
> R329 SoC has two PWM controllers in both power domains, one of
> them has 9 channels (CPUX one) and the other has 6 (CPUS one).
> 
> Add a device tree binding for them.
> 
> Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
> Signed-off-by: Aleksandr Shubin <privatesub2@gmail.com>
> ---
>  .../bindings/pwm/allwinner,sun20i-pwm.yaml    | 84 +++++++++++++++++++
>  1 file changed, 84 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/pwm/allwinner,sun20i-pwm.yaml
> 
> diff --git a/Documentation/devicetree/bindings/pwm/allwinner,sun20i-pwm.yaml b/Documentation/devicetree/bindings/pwm/allwinner,sun20i-pwm.yaml
> new file mode 100644
> index 000000000000..4b25e94a8e46
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/pwm/allwinner,sun20i-pwm.yaml
> @@ -0,0 +1,84 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/pwm/allwinner,sun20i-pwm.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Allwinner D1, T113-S3 and R329 PWM
> +
> +maintainers:
> +  - Aleksandr Shubin <privatesub2@gmail.com>
> +  - Brandon Cheo Fusi <fusibrandon13@gmail.com>
> +
> +properties:
> +  compatible:
> +    oneOf:
> +      - const: allwinner,sun20i-d1-pwm
> +      - items:
> +          - const: allwinner,sun50i-r329-pwm
> +          - const: allwinner,sun20i-d1-pwm
> +
> +  reg:
> +    maxItems: 1
> +
> +  "#pwm-cells":
> +    const: 3
> +
> +  clocks:
> +    items:
> +      - description: Bus clock
> +      - description: 24 MHz oscillator
> +      - description: APB clock
> +
> +  clock-names:
> +    items:
> +      - const: bus
> +      - const: hosc
> +      - const: apb
> +
> +  resets:
> +    maxItems: 1
> +
> +  allwinner,npwms:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    description: The number of PWM channels configured for this instance
> +    enum: [6, 8, 9]

Do we really need to be so restrictive here? The IP has an
"architectural" limit of 16 channels (due to the MMIO register layout
and status/control bits usage in some registers), so can't we just leave
this value to be anything between 1 and 16 here? If people configure
this wrongly, it's their fault, I'd say? Without confining this further
based on the respective compatible strings this enum is less useful
anyway, I think. The Allwinner A523 uses the same IP, and supports all
16 channels, the V853 implements 12, that's what I quickly found
already, and there might be more examples in the future, so I'd rather
open this up.

> +
> +allOf:
> +  - $ref: pwm.yaml#
> +
> +  - if:
> +      properties:
> +        compatible:
> +          contains:
> +            const: allwinner,sun50i-r329-pwm
> +
> +    then:
> +      required:
> +        - allwinner,npwms

Can't we just simplify this by always requiring this property? As
mentioned, there will be more SoCs with different values, so just
omitting this for the D1 seems odd.

Cheers,
Andre


> +
> +unevaluatedProperties: false
> +
> +required:
> +  - compatible
> +  - reg
> +  - "#pwm-cells"
> +  - clocks
> +  - clock-names
> +  - resets
> +
> +examples:
> +  - |
> +    #include <dt-bindings/clock/sun20i-d1-ccu.h>
> +    #include <dt-bindings/reset/sun20i-d1-ccu.h>
> +
> +    pwm: pwm@2000c00 {
> +      compatible = "allwinner,sun20i-d1-pwm";
> +      reg = <0x02000c00 0x400>;
> +      clocks = <&ccu CLK_BUS_PWM>, <&dcxo>, <&ccu CLK_APB0>;
> +      clock-names = "bus", "hosc", "apb";
> +      resets = <&ccu RST_BUS_PWM>;
> +      #pwm-cells = <0x3>;
> +    };
> +
> +...