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From: "Rafael J. Wysocki" <rafael@kernel.org>
Date: Wed, 6 Mar 2024 16:41:15 +0100
Message-ID: <CAJZ5v0gWhNqTGpoOH01scCdC51cEnt_8_T5ccqZC6yXPDv9QcA@mail.gmail.com>
Subject: Re: [RFC PATCH] thermal/core: Fix trip point crossing events ordering
To: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>, rjw@rjwysocki.net, linux-kernel@vger.kernel.org, 
	Zhang Rui <rui.zhang@intel.com>, Lukasz Luba <lukasz.luba@arm.com>, 
	"open list:THERMAL" <linux-pm@vger.kernel.org>
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On Wed, Mar 6, 2024 at 2:16=E2=80=AFPM Daniel Lezcano <daniel.lezcano@linar=
o.org> wrote:
>
> On 06/03/2024 13:53, Rafael J. Wysocki wrote:
> > On Wed, Mar 6, 2024 at 1:43=E2=80=AFPM Daniel Lezcano <daniel.lezcano@l=
inaro.org> wrote:
> >>
> >> On 06/03/2024 13:02, Rafael J. Wysocki wrote:
> >>
> >> [ ... ]
> >>
> >>>> +#define for_each_trip_reverse(__tz, __trip)    \
> >>>> +       for (__trip =3D &__tz->trips[__tz->num_trips - 1]; __trip >=
=3D __tz->trips ; __trip--)
> >>>> +
> >>>>    void __thermal_zone_set_trips(struct thermal_zone_device *tz);
> >>>>    int thermal_zone_trip_id(const struct thermal_zone_device *tz,
> >>>>                            const struct thermal_trip *trip);
> >>>> --
> >>>
> >>> Generally speaking, this is a matter of getting alignment on the
> >>> expectations between the kernel and user space.
> >>>
> >>> It looks like user space expects to get the notifications in the orde=
r
> >>> of either growing or falling temperatures, depending on the direction
> >>> of the temperature change.  Ordering the trips in the kernel is not
> >>> practical, but the notifications can be ordered in principle.  Is thi=
s
> >>> what you'd like to do?
> >>
> >> Yes
> >>
> >>> Or can user space be bothered with recognizing that it may get the
> >>> notifications for different trips out of order?
> >>
> >> IMO it is a bad information if the trip points events are coming
> >> unordered. The temperature signal is a time related measurements, the
> >> userspace should receive thermal information from this signal in the
> >> right order. It sounds strange to track the temperature signal in the
> >> kernel, then scramble the information, pass it to the userspace and
> >> except it to apply some kind of logic to unscramble it.
> >
> > So the notifications can be ordered before sending them out, as long
> > as they are produced by a single __thermal_zone_device_update() call.
> >
> > I guess you also would like the thermal_debug_tz_trip_up/down() calls
> > to be ordered, wouldn't you?
>
> Right

I have an idea how to do this, but it is based on a couple of patches
that I've been working on in the meantime.

Let me post these patches first and then I'll send a prototype patch
addressing this on top of them.