On 24/02/2020 18:39, Ondřej Jirman wrote:
> On Mon, Feb 24, 2020 at 06:23:28PM +0100, megous hlavni wrote:
>> Hi,
>>
>> On Mon, Feb 24, 2020 at 06:06:20PM +0100, Daniel Lezcano wrote:
>>> On 24/02/2020 17:54, Ondrej Jirman wrote:
>>>> This enables passive cooling by down-regulating CPU voltage
>>>> clocks = <&ccu CLK_C1CPUX>;
>>>> @@ -1188,12 +1188,60 @@ cpu0_thermal: cpu0-thermal {
>>>> polling-delay-passive = <0>;
>>>> polling-delay = <0>;
>>>> thermal-sensors = <&ths 0>;
>>>> +
>>>> + trips {
>>>> + ': cpu-hot {
>>>> + temperature = <80000>;
>>>> + hysteresis = <2000>;
>>>> + type = "passive";
>>>> + };
>>>> +
>>>> + cpu0_very_hot: cpu-very-hot {
>>>> + temperature = <100000>;
>>>> + hysteresis = <0>;
>>>> + type = "critical";
>>>> + };
>>>> + };
>>>> +
>>>> + cooling-maps {
>>>> + cpu-hot-limit {
>>>> + trip = <&cpu0_hot>;
>>>> + cooling-device = <&cpu0 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>,
>>>> + <&cpu1 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>,
>>>> + <&cpu2 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>,
>>>> + <&cpu3 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
>>>> + };
>>>> + };
>>>> };
>>>>
>>>> cpu1_thermal: cpu1-thermal {
>>>> polling-delay-passive = <0>;
>>>
>>> No polling to mitigate?
>>
>> Polling to mitigate what?
>>
>> The driver is using interrupts whenever new reading is available, and
>> notifies tz of the change. I don't have a reason to believe any new
>> values are available from thermal sensor outside of the interrupt
>> period.
>
> To be more clear, new temperatures are available from the thermal sensor driver
> at the rate of 4 per second, which should be enough to do quick adjustments to
> the thermal zone/cooling device even for quick temperature rises.
>
> https://elixir.bootlin.com/linux/v5.6-rc3/source/drivers/thermal/sun8i_thermal.c#L442
>
> There's no slow/fast period depending on whether the cooling is active.
> It's always fast and no polling of the thermal sensor is needed.
Thanks for the clarification. All sensors have their specificity.
Does the sensor allow to create a threshold temperature where an
interrupt fires when crossing the boundary? That would be interesting
for performance and energy saving to disable the interrupts until
'cpu0_hot' is reached, no?
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