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Date: Tue, 25 Aug 2020 09:25:11 +0100 From: Lukasz Luba <lukasz.luba@....com> To: Rob Herring <robh@...nel.org> Cc: Finley Xiao <finley.xiao@...k-chips.com>, heiko@...ech.de, rui.zhang@...el.com, daniel.lezcano@...aro.org, linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, devicetree@...r.kernel.org, huangtao@...k-chips.com, tony.xie@...k-chips.com, cl@...k-chips.com Subject: Re: [PATCH v1] thermal/of: Introduce k-po, k-pu and k-i for a thermal zone 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@...k-chips.com> >> --- >> 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. Only IPA uses them, thus I don't think the governors parameters: k-po, k-pu, k-i should be part of the DeviceTree. I haven't seen such governors tunnables in the DT, please point me if they exist somewhere. Do you think Rob they might be specified in the DT? Regards, Lukasz [1] https://en.wikipedia.org/wiki/PID_controller
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