RE: [PATCH v2 1/8] arm64: dts: mt8183: add thermal zone node

[Michael Kao (éæç)]

-----Original Message-----
From: Matthias Kaehlcke [mailto:mka@xxxxxxxxxxxx] 
Sent: Friday, May 31, 2019 12:08 AM
To: Hsin-Yi Wang <hsinyi@xxxxxxxxxxxx>
Cc: Michael Kao (éæç) <Michael.Kao@xxxxxxxxxxxx>; Zhang Rui <rui.zhang@xxxxxxxxx>; Eduardo Valentin <edubezval@xxxxxxxxx>; Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>; Rob Herring <robh+dt@xxxxxxxxxx>; Mark Rutland <mark.rutland@xxxxxxx>; Matthias Brugger <matthias.bgg@xxxxxxxxx>; linux-pm@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx; lkml <linux-kernel@xxxxxxxxxxxxxxx>; moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>; linux-mediatek@xxxxxxxxxxxxxxxxxxx
Subject: Re: [PATCH v2 1/8] arm64: dts: mt8183: add thermal zone node

On Thu, May 30, 2019 at 02:27:28PM +0800, Hsin-Yi Wang wrote:
> On Fri, May 10, 2019 at 9:27 PM michael.kao <michael.kao@xxxxxxxxxxxx> wrote:
> 
> > +
> > +                       tzts1: tzts1 {
> > +                               polling-delay-passive = <0>;
> > +                               polling-delay = <0>;
> > +                               thermal-sensors = <&thermal 1>;
> > +                               sustainable-power = <0>;
> > +                               trips {};
> > +                               cooling-maps {};
> > +                       };
> > +
> Is 0 a valid initial sustainable-power setting? Since we'll still get 
> warning[1] about this, though it might not be harmful.
> 
> If 0 is a valid setting, maybe we should consider showing the warning 
> of not setting this property in [2]?
> 
> [1] 
> https://elixir.bootlin.com/linux/latest/source/drivers/thermal/power_a
> llocator.c#L570 [2] 
> https://elixir.bootlin.com/linux/latest/source/drivers/thermal/of-ther
> mal.c#L1049

IIUC a value of 0 is pointless, the thermal framework will still use an estimated value:

https://elixir.bootlin.com/linux/v5.1.5/source/drivers/thermal/power_allocator.c#L203

As commented on v1 (https://patchwork.kernel.org/patch/10926519/#22620905)
the value of the property may depend on the thermal characteristics of the device, there is not one correct value per SoC/core. If it is specified at SoC level device makers should be aware that they might have to override it for 'optimal' behavior on their device.

I think there is no need to set sustainable-power for tzts1~6.
They don't bind thermal instance and will not thermal throttle.
So it will be also zero if we don't set sustainable-power and let it use estimate value.
For the purpose of preventing warning, I think I can set sustainable-power of tzts1~6 the same to cpu_thermal.