linux-kernel - Re: [PATCH 2/4] dt-bindings: arm: mediatek: Add new bindings of MediaTek frequency hopping

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Date:   Wed, 31 Aug 2022 16:19:14 +0300
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Johnson Wang <johnson.wang@...iatek.com>, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org,
        angelogioacchino.delregno@...labora.com, sboyd@...nel.org
Cc:     linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Project_Global_Chrome_Upstream_Group@...iatek.com,
        Edward-JW Yang <edward-jw.yang@...iatek.com>
Subject: Re: [PATCH 2/4] dt-bindings: arm: mediatek: Add new bindings of
 MediaTek frequency hopping

On 31/08/2022 15:48, Johnson Wang wrote:
> Add the new binding documentation for MediaTek frequency hopping
> and spread spectrum clocking control.
> 
> Co-developed-by: Edward-JW Yang <edward-jw.yang@...iatek.com>
> Signed-off-by: Edward-JW Yang <edward-jw.yang@...iatek.com>
> Signed-off-by: Johnson Wang <johnson.wang@...iatek.com>
> ---
>  .../bindings/arm/mediatek/mediatek,fhctl.yaml | 49 +++++++++++++++++++
>  1 file changed, 49 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/arm/mediatek/mediatek,fhctl.yaml
> 
> diff --git a/Documentation/devicetree/bindings/arm/mediatek/mediatek,fhctl.yaml b/Documentation/devicetree/bindings/arm/mediatek/mediatek,fhctl.yaml
> new file mode 100644
> index 000000000000..c5d76410538b
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/arm/mediatek/mediatek,fhctl.yaml
> @@ -0,0 +1,49 @@
> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/arm/mediatek/mediatek,fhctl.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: MediaTek frequency hopping and spread spectrum clocking control
> +
> +maintainers:
> +  - Edward-JW Yang <edward-jw.yang@...iatek.com>
> +
> +description: |
> +  Frequency hopping control (FHCTL) is a piece of hardware that control
> +  some PLLs to adopt "hopping" mechanism to adjust their frequency.
> +  Spread spectrum clocking (SSC) is another function provided by this hardware.
> +
> +properties:
> +  compatible:
> +    const: mediatek,fhctl

You need SoC/device specific compatibles. Preferably only SoC specific,
without generic fallback, unless you can guarantee (while representing
MediaTek), that generic fallback will cover all of their SoCs?

> +
> +  reg:
> +    maxItems: 1
> +
> +  mediatek,hopping-ssc-percents:
> +    description: |
> +      Determine the enablement of frequency hopping feature and the percentage
> +      of spread spectrum clocking for PLLs.
> +    $ref: /schemas/types.yaml#/definitions/uint32-matrix
> +    items:
> +      items:
> +        - description: PLL id that is expected to enable frequency hopping.

So the clocks are indices from some specific, yet unnamed
clock-controller? This feels hacky. You should rather take here clock
phandles (1) or integrate it into specific clock controller (2). The
reason is that either your device does something on top of existing
clocks (option 1, thus it takes clock as inputs) or it modifies existing
clocks (option 2, thus it is integral part of clock-controller).


Best regards,
Krzysztof