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