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Date: Tue, 16 May 2023 16:33:32 +0200 From: Jiri Pirko <jiri@...nulli.us> To: "Kubalewski, Arkadiusz" <arkadiusz.kubalewski@...el.com> Cc: Jakub Kicinski <kuba@...nel.org>, Vadim Fedorenko <vadfed@...a.com>, Jonathan Lemon <jonathan.lemon@...il.com>, Paolo Abeni <pabeni@...hat.com>, "Olech, Milena" <milena.olech@...el.com>, "Michalik, Michal" <michal.michalik@...el.com>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, poros <poros@...hat.com>, mschmidt <mschmidt@...hat.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>, Vadim Fedorenko <vadim.fedorenko@...ux.dev> Subject: Re: [RFC PATCH v7 1/8] dpll: spec: Add Netlink spec in YAML Tue, May 16, 2023 at 02:05:38PM CEST, arkadiusz.kubalewski@...el.com wrote: >>From: Jiri Pirko <jiri@...nulli.us> >>Sent: Monday, May 15, 2023 11:31 AM >> >>Thu, May 11, 2023 at 10:51:43PM CEST, arkadiusz.kubalewski@...el.com wrote: >>>>From: Jiri Pirko <jiri@...nulli.us> >>>>Sent: Thursday, May 11, 2023 10:00 AM >>>> >>>>Thu, May 11, 2023 at 09:40:26AM CEST, arkadiusz.kubalewski@...el.com wrote: >>>>>>From: Jakub Kicinski <kuba@...nel.org> >>>>>>Sent: Thursday, May 4, 2023 11:25 PM >>>>>> >>>>>>On Thu, 4 May 2023 14:02:30 +0200 Jiri Pirko wrote: >>>>>>> >+definitions: >>>>>>> >+ - >>>>>>> >+ type: enum >>>>>>> >+ name: mode >>>>>>> >+ doc: | >>>>>>> >+ working-modes a dpll can support, differentiate if and how dpll >>>>>>>selects >>>>>>> >+ one of its sources to syntonize with it, valid values for >>>>>>>DPLL_A_MODE >>>>>>> >+ attribute >>>>>>> >+ entries: >>>>>>> >+ - >>>>>>> >+ name: unspec >>>>>>> >>>>>>> In general, why exactly do we need unspec values in enums and CMDs? >>>>>>> What is the usecase. If there isn't please remove. >>>>>> >>>>>>+1 >>>>>> >>>>> >>>>>Sure, fixed. >>>>> >>>>>>> >+ doc: unspecified value >>>>>>> >+ - >>>>>>> >+ name: manual >>>>>> >>>>>>I think the documentation calls this "forced", still. >>>>>> >>>>> >>>>>Yes, good catch, fixed docs. >>>>> >>>>>>> >+ doc: source can be only selected by sending a request to dpll >>>>>>> >+ - >>>>>>> >+ name: automatic >>>>>>> >+ doc: highest prio, valid source, auto selected by dpll >>>>>>> >+ - >>>>>>> >+ name: holdover >>>>>>> >+ doc: dpll forced into holdover mode >>>>>>> >+ - >>>>>>> >+ name: freerun >>>>>>> >+ doc: dpll driven on system clk, no holdover available >>>>>>> >>>>>>> Remove "no holdover available". This is not a state, this is a mode >>>>>>> configuration. If holdover is or isn't available, is a runtime info. >>>>>> >>>>>>Agreed, seems a little confusing now. Should we expose the system clk >>>>>>as a pin to be able to force lock to it? Or there's some extra magic >>>>>>at play here? >>>>> >>>>>In freerun you cannot lock to anything it, it just uses system clock from >>>>>one of designated chip wires (which is not a part of source pins pool) to >>>>>feed the dpll. Dpll would only stabilize that signal and pass it further. >>>>>Locking itself is some kind of magic, as it usually takes at least ~15 >>>>>seconds before it locks to a signal once it is selected. >>>>> >>>>>> >>>>>>> >+ - >>>>>>> >+ name: nco >>>>>>> >+ doc: dpll driven by Numerically Controlled Oscillator >>>>>> >>>>>>Noob question, what is NCO in terms of implementation? >>>>>>We source the signal from an arbitrary pin and FW / driver does >>>>>>the control? Or we always use system refclk and then tune? >>>>>> >>>>> >>>>>Documentation of chip we are using, stated NCO as similar to FREERUN, and >>>>>it >>>> >>>>So how exactly this is different to freerun? Does user care or he would >>>>be fine with "freerun" in this case? My point is, isn't "NCO" some >>>>device specific thing that should be abstracted out here? >>>> >>> >>>Sure, it is device specific, some synchronizing circuits would have this >>>capability, while others would not. >>>Should be abstracted out? It is a good question.. shall user know that he is >>>in >>>freerun with possibility to control the frequency or not? >>>Let's say we remove NCO, and have dpll with enabled FREERUN mode and pins >>>supporting multiple output frequencies. >>>How the one would know if those frequencies are supported only in >>>MANUAL/AUTOMATIC modes or also in the FREERUN mode? >>>In other words: As the user can I change a frequency of a dpll if active >>>mode is FREERUN? >> >>Okay, I think I'm deep in the DPLL infra you are pushing, but my >>understanding that you can control frequency in NCO mode is not present >>:/ That only means it may be confusing and not described properly. >>How do you control this frequency exactly? I see no such knob. >> > >The set frequency is there already, although we miss phase offset I guess. Yeah, but on a pin, right? > >But I have changed my mind on having this in the kernel.. >Initially I have added this mode as our HW supports it, while thinking that >dpll subsystem shall have this, and we will implement it one day.. >But as we have not implemented it yet, let's leave work and discussion on >this mode for the future, when someone will actually try to implement it. Yeah, let's drop it then. One less confusing thing to wrap a head around :) > >>Can't the oscilator be modeled as a pin and then you are not in freerun >>but locked this "internal pin"? We know how to control frequency there. >> > >Hmm, yeah probably could work this way. > > >Thank you! >Arkadiusz > >> >>> >>>I would say it is better to have such mode, we could argue on naming though. >>> >>>> >>>>>runs on a SYSTEM CLOCK provided to the chip (plus some stabilization and >>>>>dividers before it reaches the output). >>>>>It doesn't count as an source pin, it uses signal form dedicated wire for >>>>>SYSTEM CLOCK. >>>>>In this case control over output frequency is done by synchronizer chip >>>>>firmware, but still it will not lock to any source pin signal. >>>>> >>>>>>> >+ render-max: true >>>>>>> >+ - >>>>>>> >+ type: enum >>>>>>> >+ name: lock-status >>>>>>> >+ doc: | >>>>>>> >+ provides information of dpll device lock status, valid values for >>>>>>> >+ DPLL_A_LOCK_STATUS attribute >>>>>>> >+ entries: >>>>>>> >+ - >>>>>>> >+ name: unspec >>>>>>> >+ doc: unspecified value >>>>>>> >+ - >>>>>>> >+ name: unlocked >>>>>>> >+ doc: | >>>>>>> >+ dpll was not yet locked to any valid source (or is in one of >>>>>>> >+ modes: DPLL_MODE_FREERUN, DPLL_MODE_NCO) >>>>>>> >+ - >>>>>>> >+ name: calibrating >>>>>>> >+ doc: dpll is trying to lock to a valid signal >>>>>>> >+ - >>>>>>> >+ name: locked >>>>>>> >+ doc: dpll is locked >>>>>>> >+ - >>>>>>> >+ name: holdover >>>>>>> >+ doc: | >>>>>>> >+ dpll is in holdover state - lost a valid lock or was forced by >>>>>>> >+ selecting DPLL_MODE_HOLDOVER mode >>>>>>> >>>>>>> Is it needed to mention the holdover mode. It's slightly confusing, >>>>>>> because user might understand that the lock-status is always "holdover" >>>>>>> in case of "holdover" mode. But it could be "unlocked", can't it? >>>>>>> Perhaps I don't understand the flows there correctly :/ >>>>>> >>>>>>Hm, if we want to make sure that holdover mode must result in holdover >>>>>>state then we need some extra atomicity requirements on the SET >>>>>>operation. To me it seems logical enough that after setting holdover >>>>>>mode we'll end up either in holdover or unlocked status, depending on >>>>>>lock status when request reached the HW. >>>>>> >>>>> >>>>>Improved the docs: >>>>> name: holdover >>>>> doc: | >>>>> dpll is in holdover state - lost a valid lock or was forced >>>>> by selecting DPLL_MODE_HOLDOVER mode (latter possible only >>>>> when dpll lock-state was already DPLL_LOCK_STATUS_LOCKED, >>>>> if it was not, the dpll's lock-status will remain >>>> >>>>"if it was not" does not really cope with the sentence above that. Could >>>>you iron-out the phrasing a bit please? >>> >>> >>>Hmmm, >>> name: holdover >>> doc: | >>> dpll is in holdover state - lost a valid lock or was forced >>> by selecting DPLL_MODE_HOLDOVER mode (latter possible only >>> when dpll lock-state was already DPLL_LOCK_STATUS_LOCKED, >>> if dpll lock-state was not DPLL_LOCK_STATUS_LOCKED, the >>> dpll's lock-state shall remain DPLL_LOCK_STATUS_UNLOCKED >>> even if DPLL_MODE_HOLDOVER was requested) >>> >>>Hope this is better? >> >>Okay. >> >>> >>> >>>Thank you! >>>Arkadiusz >>> >>>[...]
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