Re: [Letux-kernel] [RFC PATCH 0/3] Enable 1GHz support on omap36xx

[H. Nikolaus Schaller]

> Am 09.09.2019 um 18:38 schrieb Adam Ford <aford173@xxxxxxxxx>:
> 
> On Mon, Sep 9, 2019 at 11:32 AM Tony Lindgren <tony@xxxxxxxxxxx> wrote:
>> 
>> Hi,
>> 
>> * H. Nikolaus Schaller <hns@xxxxxxxxxxxxx> [190909 14:57]:
>>> Another question that came up by private mail from Andrà was if we
>>> should better disable the turbo OPPs of omap34xx and 36xx by default
>>> (status = "disabled";) because there are concerns about overheating
>>> the chips and we have no thermal regulation like for omap4 & 5.
> 
> I thought there was a thermal sensor?

Yes.

> 
> cpu_thermal: cpu_thermal {
>        polling-delay-passive = <250>; /* milliseconds */
>        polling-delay = <1000>; /* milliseconds */
>        coefficients = <0 20000>;
> 
>                        /* sensor       ID */
>        thermal-sensors = <&bandgap     0>;
> };
> 
> Can this driver somehow notify the cpufreq that we've hit some limit?
> I know it's not as accurate as one would like, but even for non-1GHz
> versions, having it downclock would be a good thing when running at
> extreme temps.

Indeed it is not really reliable. For me it jumps up by 10Â between first
reading within the next second (and seems to stay at this offset after first use).

But yes, I think it should be possible to use it similar to omap5-core-thermal.dtsi

Maybe we have to add "trips" and "core_crit". This must obviously be linked to
the cpufreq system. Or is it done automatically?

BR,
Nikolaus