Re: [PATCH net-next v5 1/4] dpll: add DPLL_PIN_TYPE_INT_NCO pin type

[Vadim Fedorenko <vadim.fedorenko@linux.dev>]

On 08/06/2026 16:30, Ivan Vecera wrote:
> On 6/8/26 1:33 PM, Vadim Fedorenko wrote:
>> On 04/06/2026 17:42, Ivan Vecera wrote:
>>> On 6/4/26 5:16 PM, Jakub Kicinski wrote:
>>>> On Thu, 4 Jun 2026 17:01:36 +0200 Ivan Vecera wrote:
>>>>>> Purely going on intuition here but feels like NCO should be a mode
>>>>>> (enum dpll_mode) rather than one of the input pins?
>>>>>>
>>>>>> More acks here would be great, Vadim, Arkadiusz, Grzegorz... ?
>>>>>
>>>>> I had a long discussion with Jiri about this and we agreed finally
>>>>> that dpll_mode represents a reference (input pin) selection strategy
>>>>> mode and not a DPLL device running mode.
>>>>
>>>> Long discussion? I see 2 emails ;) Let's hear from others.
>>>> (thanks for the link BTW, _if_ there's a v6 please put it in the cover
>>>> letter)
>>>
>>> I called him... he explained me 'why?' in detail.
>>> I also appreciate others' opinion.
>>
>> Well, NCO mode means manual operation of frequency tuning. Does it mean
>> that different tunings may be applied to different out pins of DPLL
>> device? My assumption that it's not possible, and in this case NCO is
>> property/mode of DPLL device rather than single pin.
> 
> The NCO pin is only one per device... When it is connected, then the
> device the pin is connected to is switched to NCO mode. In this mode
> the device is not locked to any input reference and the driver allows
> tuning of the DPLL frequency manually via PTP interface.
> 
> Such tuning is applied only to output pins associated with this device
> but not on others.
> 
> Examples:
> DPLL0 is driving output 0-3 and DPLL1 is driving output 4-7.
> Then if you switch the DPLL0 to NCO mode (makes NCO pin connected to it)
> then frequency tuning (via PTP) has only influence on output 0-3 (the
> same tuning is applied). Outputs 4-7 are not touched as they are driven
> by DPLL1 (that can be locked to some input reference).
> 
> If you switch both DPLLs to NCO, then frequency tuning for DPLL0 affects
> output 0-3 and tuning for DPLL1 output 4-7.

Technically speaking you have described per-device behavior. And NCO pin
can technically be virtual, just a configuration option via normal
device communication channel. Doesn't feel like pin's attribute. Back in
a days of DPLL RFC patches we have discussed the option with Arkadiusz,
AFAIR we were leaning towards per-DPLL state for this case.