linux-kernel - Re: [PATCH v2 1/8] arm64: dts: mt8183: add thermal zone node

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Message-ID: <20190530160825.GM40515@google.com>
Date:   Thu, 30 May 2019 09:08:25 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Hsin-Yi Wang <hsinyi@...omium.org>
Cc:     "michael.kao" <michael.kao@...iatek.com>,
        Zhang Rui <rui.zhang@...el.com>,
        Eduardo Valentin <edubezval@...il.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        lkml <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-mediatek@...ts.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@...iatek.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_allocator.c#L570
> [2] https://elixir.bootlin.com/linux/latest/source/drivers/thermal/of-thermal.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.