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
