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

[Krzysztof Kozlowski <krzk@kernel.org>]

On 21/07/2025 14:54, Ivan Vecera wrote:
> 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.

You did not address main concern. You will configure the same value for
all boards, so how do you solve uniqueness within PTP network?

> 
> 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.

It does not change anything, no problems solved.


Best regards,
Krzysztof