linux-kernel - Re: [PATCH v2] thermal: core: Add trip thresholds for trip crossing detection

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Date:   Mon, 6 Nov 2023 13:31:41 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Lukasz Luba <lukasz.luba@....com>
Subject: Re: [PATCH v2] thermal: core: Add trip thresholds for trip crossing detection

Hi Daniel,

On Mon, Nov 6, 2023 at 1:02 AM Daniel Lezcano <daniel.lezcano@...aro.org> wrote:
>
>
> Hi Rafael,
>
>
> On 03/11/2023 15:56, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >
> > The trip crossing detection in handle_thermal_trip() does not work
> > correctly in the cases when a trip point is crossed on the way up and
> > then the zone temperature stays above its low temperature (that is, its
> > temperature decreased by its hysteresis).  The trip temperature may
> > be passed by the zone temperature subsequently in that case, even
> > multiple times, but that does not count as the trip crossing as long as
> > the zone temperature does not fall below the trip's low temperature or,
> > in other words, until the trip is crossed on the way down.
> >
> > |-----------low--------high------------|
> >               |<--------->|
> >               |    hyst   |
> >               |           |
> >               |          -|--> crossed on the way up
> >               |
> >           <---|-- crossed on the way down
> >
> > However, handle_thermal_trip() will invoke thermal_notify_tz_trip_up()
> > every time the trip temperature is passed by the zone temperature on
> > the way up regardless of whether or not the trip has been crossed on
> > the way down yet.  Moreover, it will not call thermal_notify_tz_trip_down()
> > if the last zone temperature was between the trip's temperature and its
> > low temperature, so some "trip crossed on the way down" events may not
> > be reported.
> >
> > To address this issue, introduce trip thresholds equal to either the
> > temperature of the given trip, or its low temperature, such that if
> > the trip's threshold is passed by the zone temperature on the way up,
> > its value will be set to the trip's low temperature and
> > thermal_notify_tz_trip_up() will be called, and if the trip's threshold
> > is passed by the zone temperature on the way down, its value will be set
> > to the trip's temperature (high) and thermal_notify_tz_trip_down() will
> > be called.  Accordingly, if the threshold is passed on the way up, it
> > cannot be passed on the way up again until its passed on the way down
> > and if it is passed on the way down, it cannot be passed on the way down
> > again until it is passed on the way up which guarantees correct
> > triggering of trip crossing notifications.
> >
> > If the last temperature of the zone is invalid, the trip's threshold
> > will be set depending of the zone's current temperature: If that
> > temperature is above the trip's temperature, its threshold will be
> > set to its low temperature or otherwise its threshold will be set to
> > its (high) temperature.  Because the zone temperature is initially
> > set to invalid and tz->last_temperature is only updated by
> > update_temperature(), this is sufficient to set the correct initial
> > threshold values for all trips.
> >
> > Link: https://lore.kernel.org/all/20220718145038.1114379-4-daniel.lezcano@linaro.org
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > ---
> >
> > v1 (RFC) -> v2: Add missing description of a new struct thermal_trip field.
> >
> > And because no comments have been sent for a week, this is not an RFC
> > any more.
>
> Can you give me a few days to review this patch and test it with some
> debugfs code planned to be submitted?

Sure, I'm not going to do anything with it until 6.7-rc1 is out anyway.

Thanks!