Re: [PATCH net-next v4 1/3] dpll: add reference-sync netlink attribute

[Jakub Kicinski <kuba@kernel.org>]

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?

> +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.