Re: [PATCH RFC 1/3] dt-bindings: clock: Add Renesas versa3 clock generator bindings

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Hi Krzysztof,

On Thu, Mar 9, 2023 at 11:17 AM Krzysztof Kozlowski
<krzysztof.kozlowski@xxxxxxxxxx> wrote:
> On 09/03/2023 10:58, Geert Uytterhoeven wrote:
> >>>>> Here it is, Please let me know is it ok?
> >>>>>
> >>>>> renesas,output-clock-fixed-rate-mode:
> >>>>>     type: boolean
> >>>>>     description:
> >>>>>       In output clock fixed rate mode, the output clock frequency is
> >>>> always
> >>>>>       fixed and the hardware will use the values from the OTP or full
> >>>> register
> >>>>>     map initialized during boot.
> >>>>>       If not given, the output clock rate is not fixed.
> >>>>>     maxItems: 6
> >>>>
> >>>> boolean is scalar, not array, so no maxItems. If the frequency is taken from
> >>>> OTP or register map, why they cannot also provide information the clock is
> >>>> fixed?
> >>>
> >>> OK, I will make an array property instead. From HW perspective each clock output from the
> >>> Clock generator is controllable ie, fixed rate or dynamic rate.
> >>>
> >>> If all the output clocks are fixed rate one, then frequency is taken from OTP or
> >>> register map. But if any one clock output generates dynamic rate, then it uses
> >>> dynamic settings.
> >>
> >> Second try, same question, let me know if it is not clear:
> >>
> >> "why they cannot also provide information the clock is fixed?"
> >
> > What is the actual use case?
> > My understanding is:
> >   1. If the OTP is programmed, the clock generator will be configured
> >      from the OTP on power-on,
> >   2. The clock generator can be (re)configured from software.
> >      a. If the OTP is programmed, this is not needed,
> >      b. For critical clocks, you may want to prevent this.
> >
> > Also, AFAIUI, "fixed frequency" or "dynamic frequency" is a policy,
> > and purely software? Or are there OTP bits to enforce this?
> >
> > Perhaps you need a per-output "do-not-change-frequency" flag,
> > probably with a generic name, in the spirit of "regulator-always-on"
> > for regulators?

Actually we already have "assigned-clock{,-rate}s" properties for that.

> > Now, if all the output clocks are fixed rate, you might want to describe
> > this in DTS using a set of fixed{,-factor-}-clocks?
>
> I would also argue that fixed frequency is actually also dynamic
> frequency, just with a limit to one frequency...

Indeed.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds



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