linux-kernel - Re: [PATCH net-next 1/2] dt-bindings: dpll: Add clock ID property

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Message-ID: <1419bca0-b85a-4d4b-af1a-b0540c25933a@lunn.ch>
Date: Mon, 4 Aug 2025 20:45:05 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Ivan Vecera <ivecera@...hat.com>
Cc: Krzysztof Kozlowski <krzk@...nel.org>, netdev@...r.kernel.org,
	Vadim Fedorenko <vadim.fedorenko@...ux.dev>,
	Arkadiusz Kubalewski <arkadiusz.kubalewski@...el.com>,
	Jiri Pirko <jiri@...nulli.us>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Prathosh Satish <Prathosh.Satish@...rochip.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	Michal Schmidt <mschmidt@...hat.com>, Petr Oros <poros@...hat.com>
Subject: Re: [PATCH net-next 1/2] dt-bindings: dpll: Add clock ID property

> Let's say we have a SyncE setup with two network controllers where each
> of them feeds a DPLL channel with recovered clock received from some of
> its PHY. The DPLL channel cleans/stabilizes this input signal (generates
> phase aligned signal locked to the same frequency as the input one) and
> routes it back to the network controller.
> 
>     +-----------+
>  +--|   NIC 1   |<-+
>  |  +-----------+  |
>  |                 |
>  | RxCLK     TxCLK |
>  |                 |
>  |  +-----------+  |
>  +->| channel 1 |--+
>     |-- DPLL ---|
>  +->| channel 2 |--+
>  |  +-----------+  |
>  |                 |
>  | RxCLK     TxCLK |
>  |                 |
>  |  +-----------+  |
>  +--|   NIC 2   |<-+
>     +-----------+
> 
> The PHCs implemented by the NICs have associated the ClockIdentity
> (according IEEE 1588-2008) whose value is typically derived from
> the NIC's MAC address using EUI-64. The DPLL channel should be
> registered to DPLL subsystem using the same ClockIdentity as the PHC
> it drives. In above example DPLL channel 1 should have the same clock ID
> as NIC1 PHC and channel 2 as NIC2 PHC.
> 
> During the discussion, Andrew had the idea to provide NIC phandles
> instead of clock ID values.
> 
> Something like this:
> 
> diff --git a/Documentation/devicetree/bindings/dpll/dpll-device.yaml
> b/Documenta
> tion/devicetree/bindings/dpll/dpll-device.yaml
> index fb8d7a9a3693f..159d9253bc8ae 100644
> --- a/Documentation/devicetree/bindings/dpll/dpll-device.yaml
> +++ b/Documentation/devicetree/bindings/dpll/dpll-device.yaml
> @@ -33,6 +33,13 @@ properties:
>      items:
>        enum: [pps, eec]
> 
> +  ethernet-handles:
> +    description:
> +      List of phandles to Ethernet devices, one per DPLL instance. Each of
> +      these handles identifies Ethernet device that uses particular DPLL
> +      instance to synchronize its hardware clock.
> +    $ref: /schemas/types.yaml#/definitions/phandle-array
> +

I personally would not use a list. I would have a node per channel,
and within that node, have the ethernet-handle property. This gives
you a more flexible scheme where you can easily add more per channel
properties in the future.

It took us a while to understand what you actually wanted. The ASCII
art helps. So i would include that and some text in the binding.

	Andrew