Is cpufreq-dt safe without regulator support?

[wens Tsai]

On Tue, Mar 17, 2015 at 4:47 PM, Viresh Kumar <viresh.kumar at linaro.org> wrote:
> On 17 March 2015 at 13:15, wens Tsai <wens213 at gmail.com> wrote:
>> The sunxi platform added cpufreq support in 4.0.0-rc1 using
>> the generic cpufreq-dt driver. One issue we've run into is
>> the default OPPs we use include an overclocked/overvoltage
>> setting.
>
> There is a feature for that in cpufreq, in case you don't know, "boost"..

I do now. Though cpufreq-dt and the OPP bindings don't
support this. Any chance the next version of OPP bindings will?

>> If the cpu is missing a regulator supply phandle, or the
>> kernel is built without regulators, cpufreq can increase
>> the clock rate without the needed voltage increase.
>
> Right.
>
>> The former issue can be resolved by providing a dummy
>> regulator with the default voltage, effectively disabling
>> cpufreq.
>
> How ? CPUFreq will try to change both volt and freq. Volt
> wouldn't change as its a dummy regulator, but freq would
> still be changed..

I suppose this is the desired behavior. I'm fine with it then.

>> The latter is possible. Without regulator support built-in,
>> even a correct, complete DTS can still fail. Should I just
>> remove the offending OPP? Still that does not fix the
>> problem when we actually do want overclocking.
>>
>> To summarize, should cpufreq-dt probe fail when regulator
>> support isn't available? Should we differentiate between
>
> No. We can have regulator support enabled but no regulator
> for a CPU. And so the current state of code looks fine.
>
>> not having a regulator phandle vs no regulator support?
>
> What I couldn't understand is, why would you miss the regulator
> phandle in dts? Or not compile regulator support?

I admit it is partly bad execution on my part. I added the OPPs
to the .dtsi files, but only the regulators to a handful of boards
that I have. All the other boards do not have a regulator phandle.

> In case you want cpufreq-dt to be disabled if regulators aren't
> compiled in, then what you should do is, don't create the platform
> device required for probing cpufreq-dt driver.

Thanks for the suggestion. I'll add if(IS_ENABLED()) around it.
I can also check for the regulator phandle here.

Regards
ChenYu