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

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Date:   Mon, 6 Nov 2023 01:02:30 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>
Cc:     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 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?

Thanks


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