On Tue, Aug 25, 2020 at 3:44 AM Daniel Lezcano <daniel.lezcano@xxxxxxxxxx> wrote: > > On 25/08/2020 10:25, Lukasz Luba wrote: > > Hi Rob, > > > > On 8/25/20 12:09 AM, Rob Herring wrote: > >> On Tue, Aug 11, 2020 at 08:31:15PM +0800, Finley Xiao wrote: > >>> The default value for k_pu is: > >>> 2 * sustainable_power / (desired_temperature - switch_on_temp) > >>> The default value for k_po is: > >>> sustainable_power / (desired_temperature - switch_on_temp) > >>> The default value for k_i is 10. > >>> > >>> Even though these parameters of the PID controller can be changed > >>> by the following sysfs files: > >>> /sys/class/thermal/thermal_zoneX/k_pu > >>> /sys/class/thermal/thermal_zoneX/k_po > >>> /sys/class/thermal/thermal_zoneX/k_i > >>> > >>> But it's still more convenient to change the default values by > >>> devicetree, > >>> so introduce these three optional properties. If provided these > >>> properties, > >>> they will be parsed and associated with the thermal zone via the thermal > >>> zone parameters. > >>> > >>> Signed-off-by: Finley Xiao <finley.xiao@xxxxxxxxxxxxxx> > >>> --- > >>> Documentation/devicetree/bindings/thermal/thermal.txt | 14 > >>> ++++++++++++++ > >> > >> Bindings should be a separate file and this one is a DT schema now. > >> > >>> drivers/thermal/thermal_of.c | 7 +++++++ > >>> 2 files changed, 21 insertions(+) > >>> > >>> diff --git a/Documentation/devicetree/bindings/thermal/thermal.txt > >>> b/Documentation/devicetree/bindings/thermal/thermal.txt > >>> index f78bec19ca35..ebe936b57ded 100644 > >>> --- a/Documentation/devicetree/bindings/thermal/thermal.txt > >>> +++ b/Documentation/devicetree/bindings/thermal/thermal.txt > >>> @@ -165,6 +165,20 @@ Optional property: > >>> 2000mW, while on a 10'' tablet is around > >>> 4500mW. > >>> +- k-po: Proportional parameter of the PID controller when > >>> + current temperature is above the target. > >>> + Type: signed > >>> + Size: one cell > >>> + > >>> +- k-pu: Proportional parameter of the PID controller when > >>> + current temperature is below the target. > >>> + Type: signed > >>> + Size: one cell > >>> + > >>> +- k-i: Integral parameter of the PID controller. > >>> + Type: signed > >>> + Size: one cell > >> > >> What's PID? > >> > >> I know nothing about the sysfs params, but the binding needs to stand on > >> it's own and needs enough detail to educate me. > > Sorry for the delay, I missed that patch. > > These parameters are the coefficients for the > > Proportional-Integral-Derivative (PID) controller [1], which is the > > core of the Intelligent Power Allocation (IPA) thermal governor. > > Just a few words to elaborate a bit for Rob who may not have time to > digest the whole concept from Wikipedia :) > > The PID is an regulation loop where the input is compared to the output. > > For example when driving a car and you aim a speed cruise of 90km/h. You > press the accelerator and watch the current speed. The smaller the > current speed is, the stronger you will push the accelerator. And the > closer to the cruise speed the car is, the lesser you push the > accelerator until the car stabilize to the cruise to speed. > > The k-* describes how strong you push the accelerator and release it. > > In the thermal framework, that has an impact on how brutal the > mitigation acts and depending on them it results in a flat temperature > curve or a sawtooth aspect. > > These coefficient depends on the ambient temperature (casing, room > temperature), the heat sink and the load. Depending on the use cases, > you may want to change their values at runtime. > > From my POV, setting these values in the DT does not really make sense. I pretty much always agree with not putting things in DT. :) Rob
