Message-ID: <804b4a5f-06bc-4943-8801-2582463c28ef@redhat.com>
Date: Mon, 21 Jul 2025 14:54:04 +0200
From: Ivan Vecera <ivecera@...hat.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: 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

On 21. 07. 25 11:23 dop., Krzysztof Kozlowski wrote:
> On Fri, Jul 18, 2025 at 02:16:41PM +0200, Ivan Vecera wrote:
>> Hi Krzysztof,
>>
>> ...
>>
>> The clock-id property name may have been poorly chosen. This ID is used by
>> the DPLL subsystem during the registration of a DPLL channel, along with its
>> channel ID. A driver that provides DPLL functionality can compute this
>> clock-id from any unique chip information, such as a serial number.
>>
>> Currently, other drivers that implement DPLL functionality are network
>> drivers, and they generate the clock-id from one of their MAC addresses by
>> extending it to an EUI-64.
>>
>> A standalone DPLL device, like the zl3073x, could use a unique property such
>> as its serial number, but the zl3073x does not have one. This patch-set is
>> motivated by the need to support such devices by allowing the DPLL device ID
>> to be passed via the Device Tree (DT), which is similar to how NICs without
>> an assigned MAC address are handled.
> 
> You use words like "unique" and MAC, thus I fail to see how one fixed
> string for all boards matches this. MACs are unique. Property value set
> in DTS for all devices is not.
>> You also need to explain who assigns this value (MACs are assigned) or
> if no one, then why you cannot use random? I also do not see how this
> property solves this...  One person would set it to value "1", other to
> "2" but third decide to reuse "1"? How do you solve it for all projects
> in the upstream?

Some background: Any DPLL driver has to use a unique number during the
DPLL device/channel registration. The number must be unique for the
device across a clock domain (e.g., a single PTP network).

NIC drivers that expose DPLL functionality usually use their MAC address
to generate such a unique ID. A standalone DPLL driver does not have
this option, as there are no NIC ports and therefore no MAC addresses.
Such a driver can use any other source for the ID (e.g., the chip's
serial number). Unfortunately, this is not the case for zl3073x-based
hardware, as its current firmware revisions do not expose information
that could be used to generate the clock ID (this may change in the
future).

There is no authority that assigns clock ID value ranges similarly to
MAC addresses (OUIs, etc.), but as mentioned above, uniqueness is
required across a single PTP network so duplicates outside this
single network are not a problem.

A randomly generated clock ID works, but the problem is that the value
is different after each reboot. Yes, there is an option to override the
clock ID using the devlink interface, but this also has to be done after
every reboot or power-up.

> All this must be clearly explained when you add new, generic property.

Would it be acceptable to define a hardware-specific property, since
only this hardware has this particular problem (the absence of a chip
unique attribute)? I'm referring to a property like 'microchip,id' or
'microchip,dpll-id' defined in microchip,zl30731.yaml.

> Best regards,
> Krzysztof

Thanks,
Ivan

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