[PATCH 1/2] clk: scpi: RfC - Allow to ignore invalid SCPI DVFS clock rates

[Sudeep Holla]

On 09/02/17 12:19, Michał Zegan wrote:
> 
> 
> W dniu 09.02.2017 o 11:52, Sudeep Holla pisze:
>>
>>
>> On 08/02/17 19:45, Kevin Hilman wrote:
>>> Sudeep Holla <sudeep.holla at arm.com> writes:
>>>
>>>> On 04/02/17 21:03, Heiner Kallweit wrote:
>>>>> Introduce an optional property "clock-max-frequency" for SCPI DVFS
>>>>> clocks. All frequencies for the respective clock exceeding this
>>>>> threshold will be ignored.
>>>>>
>>>>> This is useful on systems where the firmware offers too optimistic
>>>>> clock rates causing instabilities and crashes.
>>>>>
>>>>
>>>> It clearly means the firmware/hardware(IOW platform) was not tested
>>>> correctly before firmware advertised the OPPs. It needs to fixed in the
>>>> firmware. The approach should be advertise the known minimal set working
>>>> rather than the set for which hardware was designed.
>>>>
>>>> That's the whole reason while these are kept in firmware so the OS need
>>>> not worry about such details.
>>>>
>>>> So NACK, go fix the firmware 
>>>
>>> Sorry, but "go fix the firmware" is not an option for most users of
>>> these boards.
>>>
>>
>> I knew this was coming :). I just wanted to shout at vendors who are not
>> validating their firmware. Sometimes I feel it's better have platform
>> driver and drive everything from Linux and don't use buggy firmware at
>> all instead of adding tons of workaround. It defeats the whole purpose
>> of having the firmware.
>>
> Well, at least in the case of odroid c2 from hardkernel, I believe those
> unstable frequencies are supported intentionally. The wiki of the board
> lists them explicitly, and says when they are stable.
> So if that was intentional, then a frequency capping set by default
> would be needed, it can be lifted by a specific user if he wants. Unless
> hk should disable that "feature" instead.

If those frequency are known to cause any stability issues, they should
be considered as *not supported*. If it's just thermal constraints then
yes the user/developer should be allowed to use them as they can take
care of thermal management so that the platform remains stable for usage.

-- 
Regards,
Sudeep