linux-kernel - Re: [PATCH v3 4/7] thermal/drivers/tegra: Add driver for Tegra30 thermal sensor

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Message-ID: <20210615102626.dja3agclwzxv2sj4@vireshk-i7>
Date:   Tue, 15 Jun 2021 15:56:26 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     Dmitry Osipenko <digetx@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Zhang Rui <rui.zhang@...el.com>,
        Amit Kucheria <amitk@...nel.org>,
        Andreas Westman Dorcsak <hedmoo@...oo.com>,
        Maxim Schwalm <maxim.schwalm@...il.com>,
        Svyatoslav Ryhel <clamor95@...il.com>,
        Ihor Didenko <tailormoon@...bler.ru>,
        Ion Agorria <ion@...rria.com>,
        Matt Merhar <mattmerhar@...tonmail.com>,
        Peter Geis <pgwipeout@...il.com>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH v3 4/7] thermal/drivers/tegra: Add driver for Tegra30
 thermal sensor

On 15-06-21, 12:03, Daniel Lezcano wrote:
> 
> [Cc Viresh]
> 
> On 29/05/2021 19:09, Dmitry Osipenko wrote:
> > All NVIDIA Tegra30 SoCs have a two-channel on-chip sensor unit which
> > monitors temperature and voltage of the SoC. Sensors control CPU frequency
> > throttling, which is activated by hardware once preprogrammed temperature
> > level is breached, they also send signal to Power Management controller to
> > perform emergency shutdown on a critical overheat of the SoC die. Add
> > driver for the Tegra30 TSENSOR module, exposing it as a thermal sensor
> > and a cooling device.
> 
> IMO it does not make sense to expose the hardware throttling mechanism
> as a cooling device because it is not usable anywhere from the thermal
> framework.
> 
> Moreover, that will collide with the thermal / cpufreq framework
> mitigation (hardware sets the frequency but the software thinks the freq
> is different), right ?

I am not even sure what the cooling device is doing here:

tegra_tsensor_set_cur_state() is not implemented and it says hardware
changed it by itself. What is the benefit you are getting out of the
cooling device here ?

> The hardware limiter should let know the cpufreq framework about the
> frequency change.
> 
> 	https://lkml.org/lkml/2021/6/8/1792
> 
> May be post the sensor without the hw limiter for now and address that
> in a separate series ?

-- 
viresh