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

[Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>]

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?
> 
> 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...

Best regards,
Krzysztof