RE: [Intel-wired-lan] [PATCH net-next v4 1/3] dpll: add reference-sync netlink attribute

[Kubalewski, Arkadiusz]

>From: Intel-wired-lan <intel-wired-lan-bounces@xxxxxxxxxx> On Behalf Of
>Jakub Kicinski
>Sent: Friday, May 30, 2025 2:49 AM
>
>On Fri, 23 May 2025 19:26:48 +0200 Arkadiusz Kubalewski wrote:
>> +The device may support the Reference SYNC feature, which allows the
>>combination
>> +of two inputs into a Reference SYNC pair. In this configuration, clock
>>signals
>> +from both inputs are used to synchronize the dpll device. The higher
>>frequency
>> +signal is utilized for the loop bandwidth of the DPLL, while the lower
>>frequency
>> +signal is used to syntonize the output signal of the DPLL device. This
>>feature
>> +enables the provision of a high-quality loop bandwidth signal from an
>>external
>> +source.
>
>I'm uninitiated into the deeper arts of time sync, but to me this
>sounds like a reference clock. Are you trying not to call it clock
>because in time clock means a ticker, and this is an oscillator?
>

We shall refer to a reference clock for each input pin, right?
TBH, I have reused the name from dpll chip docs, I believe they have
tried to make similar features and naming convention for both:
Embedded SYNC/Reference SYNC, and that makes some sense.

>> +A capable input provides a list of inputs that can be paired to create a
>> +Reference SYNC pair. To control this feature, the user must request a
>>desired
>> +state for a target pin: use ``DPLL_PIN_STATE_CONNECTED`` to enable or
>> +``DPLL_PIN_STATE_DISCONNECTED`` to disable the feature. Only two pins
>>can be
>> +bound to form a Reference SYNC pair at any given time.
>
>Mostly I got confused by the doc saying "Reference SYNC pair".
>I was expecting that you'll have to provide 2 ref sync signals.
>But IIUC the first signal is still the existing signal we lock
>into, so the pair is of a reference sync + an input pin?
>Not a pair of two reference syncs.
>
>IOW my reading of the doc made me expect 2 pins to always be passed in
>as ref sync, but the example from the cover letter shows only adding
>one.

Yes, exactly, will try to improve this in next version.

Thank you!
Arkadiusz