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

From: Ivan Vecera
Date: Fri Aug 29 2025 - 09:29:41 EST

Hi Rob,

On 20. 08. 25 11:13 odp., Rob Herring wrote:
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.

Suggested-by: Andrew Lunn <andrew@xxxxxxx>
Signed-off-by: Ivan Vecera <ivecera@xxxxxxxxxx>
---
.../devicetree/bindings/dpll/dpll-device.yaml | 40 ++++++++++++++++---
.../bindings/dpll/microchip,zl30731.yaml | 29 +++++++++++++-
2 files changed, 62 insertions(+), 7 deletions(-)

diff --git a/Documentation/devicetree/bindings/dpll/dpll-device.yaml b/Documentation/devicetree/bindings/dpll/dpll-device.yaml
index fb8d7a9a3693f..798c5484657cf 100644
--- a/Documentation/devicetree/bindings/dpll/dpll-device.yaml
+++ b/Documentation/devicetree/bindings/dpll/dpll-device.yaml
@@ -27,11 +27,41 @@ properties:
"#size-cells":
const: 0
- dpll-types:
- description: List of DPLL channel types, one per DPLL instance.
- $ref: /schemas/types.yaml#/definitions/non-unique-string-array
- items:
- enum: [pps, eec]

Dropping this is an ABI change. You can't do that unless you are
confident there are no users both in existing DTs and OSs.

Get it, will keep.

+ channels:
+ type: object
+ description: DPLL channels
+ unevaluatedProperties: false
+
+ properties:
+ "#address-cells":
+ const: 1
+ "#size-cells":
+ const: 0
+
+ patternProperties:
+ "^channel@[0-9a-f]+$":
+ type: object
+ description: DPLL channel
+ unevaluatedProperties: false
+
+ properties:
+ reg:
+ description: Hardware index of the DPLL channel
+ maxItems: 1
+
+ dpll-type:
+ description: DPLL channel type
+ $ref: /schemas/types.yaml#/definitions/string
+ enum: [pps, eec]
+
+ ethernet-handle:
+ description:
+ Specifies a reference to a node representing an Ethernet device
+ that uses this channel to synchronize its hardware clock.
+ $ref: /schemas/types.yaml#/definitions/phandle

Seems a bit odd to me that the ethernet controller doesn't have a link
to this node instead.

Do you mean to add a property (e.g. dpll-channel or dpll-device) into
net/network-class.yaml ? If so, yes, it would be possible, and the way
I look at it now, it would probably be better. The DPLL driver can
enumerate all devices across the system that has this specific property
and check its value.

See the proposal below...

Thanks,
Ivan

---
Documentation/devicetree/bindings/dpll/dpll-device.yaml | 6 ++++++
Documentation/devicetree/bindings/net/network-class.yaml | 7 +++++++
2 files changed, 13 insertions(+)

diff --git a/Documentation/devicetree/bindings/dpll/dpll-device.yaml b/Documentation/devicetree/bindings/dpll/dpll-device.yaml
index fb8d7a9a3693f..560351df1bec3 100644
--- a/Documentation/devicetree/bindings/dpll/dpll-device.yaml
+++ b/Documentation/devicetree/bindings/dpll/dpll-device.yaml
@@ -27,6 +27,12 @@ properties:
"#size-cells":
const: 0

+ "#dpll-cells":
+ description: |
+ Number of cells in a dpll specifier. The cell specifies the index
+ of the channel within the DPLL device.
+ const: 1
+
dpll-types:
description: List of DPLL channel types, one per DPLL instance.
$ref: /schemas/types.yaml#/definitions/non-unique-string-array
diff --git a/Documentation/devicetree/bindings/net/network-class.yaml b/Documentation/devicetree/bindings/net/network-class.yaml
index 06461fb92eb84..144badb3b7ff1 100644
--- a/Documentation/devicetree/bindings/net/network-class.yaml
+++ b/Documentation/devicetree/bindings/net/network-class.yaml
@@ -17,6 +17,13 @@ properties:
default: 48
const: 48

+ dpll:
+ description:
+ Specifies DPLL device phandle and index of the DPLL channel within
+ this device used by this network device to synchronize its hardware
+ clock.
+ $ref: /schemas/types.yaml#/definitions/phandle
+
local-mac-address:
description:
Specifies MAC address that was assigned to the network device described by