linux-kernel - Re: [RFC PATCH net-next] dt-bindings: dpll: Add per-channel Ethernet reference property

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Message-ID: <366b1990-78b2-483f-bda5-2958274939e4@lunn.ch>
Date: Sat, 16 Aug 2025 01:21:17 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Ivan Vecera <ivecera@...hat.com>
Cc: netdev@...r.kernel.org, mschmidt@...hat.com, poros@...hat.com,
	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>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" <devicetree@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH net-next] dt-bindings: dpll: Add per-channel Ethernet
 reference property

On Fri, Aug 15, 2025 at 04:47:35PM +0200, Ivan Vecera wrote:
> In case of SyncE scenario a DPLL channels generates a clean frequency
> synchronous Ethernet clock (SyncE) and feeds it into the NIC transmit
> path. The DPLL channel can be locked either to the recovered clock
> from the NIC's PHY (Loop timing scenario) or to some external signal
> source (e.g. GNSS) (Externally timed scenario).
> 
> The example shows both situations. NIC1 recovers the input SyncE signal
> that is used as an input reference for DPLL channel 1. The channel locks
> to this signal, filters jitter/wander and provides holdover. On output
> the channel feeds a stable, phase-aligned clock back into the NIC1.
> In the 2nd case the DPLL channel 2 locks to a master clock from GNSS and
> feeds a clean SyncE signal into the NIC2.
> 
> 		   +-----------+
> 		+--|   NIC 1   |<-+
> 		|  +-----------+  |
> 		|                 |
> 		| RxCLK     TxCLK |
> 		|                 |
> 		|  +-----------+  |
> 		+->| channel 1 |--+
> +------+	   |-- DPLL ---|
> | GNSS |---------->| channel 2 |--+
> +------+  RefCLK   +-----------+  |
> 				  |
> 			    TxCLK |
> 				  |
> 		   +-----------+  |
> 		   |   NIC 2   |<-+
> 		   +-----------+
> 
> In the situations above the DPLL channels should be registered into
> the DPLL sub-system with the same Clock Identity as PHCs present
> in the NICs (for the example above DPLL channel 1 uses the same
> Clock ID as NIC1's PHC and the channel 2 as NIC2's PHC).
> 
> Because a NIC PHC's Clock ID is derived from the NIC's MAC address,
> add a per-channel property 'ethernet-handle' that specifies a reference
> to a node representing an Ethernet device that uses this channel
> to synchronize its hardware clock. Additionally convert existing
> 'dpll-types' list property to 'dpll-type' per-channel property.

It would be normal to include an implementation of the binding as
patch 2/2. Looking at the implementation sometimes makes
errors/omission in the binding obvious.

> +        channels {
> +          #address-cells = <1>;
> +          #size-cells = <0>;
> +
> +          channel@0 {
> +            reg = <0>;
> +            dpll-type = "pps";
> +          };
> +
> +          channel@1 {
> +            reg = <1>;
> +            dpll-type = "eec";
> +            ethernet-handle = <&ethernet0>;
> +          };

If i'm reading this correctly, eec requires a ethernet-handle. pps
does not. You should describe that in the binding using constraints.

Otherwise, this looks reasonable to me.

	   Andrew