linux-kernel - Re: [PATCH RESEND v2 2/5] thermal/drivers/mediatek/lvts: Disable Stage 3 thermal threshold

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Message-ID: <a61835ca-a13d-4547-b3a2-3563688bff25@notapiano>
Date: Thu, 16 Jan 2025 10:27:00 -0300
From: Nícolas F. R. A. Prado <nfraprado@...labora.com>
To: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
	Zhang Rui <rui.zhang@...el.com>, Lukasz Luba <lukasz.luba@....com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Alexandre Mergnat <amergnat@...libre.com>,
	Balsam CHIHI <bchihi@...libre.com>, kernel@...labora.com,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org,
	Hsin-Te Yuan <yuanhsinte@...omium.org>,
	Chen-Yu Tsai <wenst@...omium.org>,
	Bernhard Rosenkränzer <bero@...libre.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	stable@...r.kernel.org
Subject: Re: [PATCH RESEND v2 2/5] thermal/drivers/mediatek/lvts: Disable
 Stage 3 thermal threshold

On Tue, Jan 14, 2025 at 12:54:43PM +0100, Daniel Lezcano wrote:
> On 13/01/2025 14:27, Nícolas F. R. A. Prado wrote:
> > The Stage 3 thermal threshold is currently configured during
> > the controller initialization to 105 Celsius. From the kernel
> > perspective, this configuration is harmful because:
> > * The stage 3 interrupt that gets triggered when the threshold is
> >    crossed is not handled in any way by the IRQ handler, it just gets
> >    cleared. Besides, the temperature used for stage 3 comes from the
> >    sensors, and the critical thermal trip points described in the
> >    Devicetree will already cause a shutdown when crossed (at a lower
> >    temperature, of 100 Celsius, for all SoCs currently using this
> >    driver).
> > * The only effect of crossing the stage 3 threshold that has been
> >    observed is that it causes the machine to no longer be able to enter
> >    suspend. Even if that was a result of a momentary glitch in the
> >    temperature reading of a sensor (as has been observed on the
> >    MT8192-based Chromebooks).
> > 
> > For those reasons, disable the Stage 3 thermal threshold configuration.
> 
> Does this stage 3 not designed to reset the system ? So the interrupt line
> should be attached to the reset line ? (just asking)

Yes, my guess is that the intention of stage 3 is to cause a system reset,
however it clearly does not cause a system reset, so it is not directly
connected to the reset line in any way. Instead it is up to the kernel to
receive the interrupt and deal with it. But then, since there are lower thermal
thresholds that already cause a system shutdown, it's useless to keep this
around - it only causes suspend/resume misbehaviors in case there are spurious
readings.

Thanks,
Nícolas