linux-kernel - Re: [PATCH v2 01/14] thermal/core: Change thermal_zone_ops to thermal_sensor

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Message-ID: <CAJZ5v0gBm+rEkAZ-9DGoR5Z0HS=D-b_XeJSyUUX6Ui5sgh7MwQ@mail.gmail.com>
Date:   Tue, 17 May 2022 21:07:14 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     srinivas pandruvada <srinivas.pandruvada@...ux.intel.com>
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Subject: Re: [PATCH v2 01/14] thermal/core: Change thermal_zone_ops to thermal_sensor_ops

On Tue, May 17, 2022 at 9:02 PM srinivas pandruvada
<srinivas.pandruvada@...ux.intel.com> wrote:
>
> On Tue, 2022-05-17 at 20:53 +0200, Rafael J. Wysocki wrote:
> > On Tue, May 17, 2022 at 6:51 PM srinivas pandruvada
> > <srinivas.pandruvada@...ux.intel.com> wrote:
> > >
> > > On Tue, 2022-05-17 at 17:42 +0200, Rafael J. Wysocki wrote:
> > > > On Sat, May 7, 2022 at 2:55 PM Daniel Lezcano
> > > > <daniel.lezcano@...exp.org> wrote:
> > > > >
> > > > > A thermal zone is software abstraction of a sensor associated
> > > > > with
> > > > > properties and cooling devices if any.
> > > > >
> > > > > The fact that we have thermal_zone and thermal_zone_ops mixed
> > > > > is
> > > > > confusing and does not clearly identify the different
> > > > > components
> > > > > entering in the thermal management process. A thermal zone
> > > > > appears
> > > > > to
> > > > > be a sensor while it is not.
> > > >
> > > > Well, the majority of the operations in thermal_zone_ops don't
> > > > apply
> > > > to thermal sensors.  For example, ->set_trips(), -
> > > > >get_trip_type(),
> > > > ->get_trip_temp().
> > > >
> > > In past we discussed adding thermal sensor sysfs with threshold to
> > > notify temperature.
> > >
> > > So sensor can have set/get_threshold() functions instead of the
> > > set/get_trip for zones.
> > >
> > > Like we have /sys/class/thermal_zone* we can have
> > > /sys/class/thermal_sensor*.
> >
> > Exactly, so renaming thermal_zone_ops as thermal_sensor_ops isn't
> > quite helpful in this respect.
> >
> > IMO there should be operations for sensors and there should be
> > operations for thermal zones and those two sets of operations should
> > be different.
> >
> > > Thermal sensor(s) are bound to  thermal zones.
> >
> > So I think that this binding should be analogous to the binding
> > between thermal zones and cooling devices.
> >
> > > This can also include multiple sensors in a zone and can create a
> > > virtual sensor also.
> >
> > It can.
> >
> > However, what's the difference between a thermal zone with multiple
> > sensors and a thermal zone with one virtual sensor being an aggregate
> > of multiple physical sensors?
> >
> Either way is fine. A thermal sensor can be aggregate of other sensors.

Agreed.

But the point is that if we go with thermal zones bound to multiple
physical sensors, I don't see much point in using virtual sensors.
And the other way around.

Daniel seems to be preferring the thermal zones bound to multiple
physical sensors approach.


> > Both involve some type of aggregation of temperature values measured
> > by the physical sensors.
> >
> > > > > In order to set the scene for multiple thermal sensors
> > > > > aggregated
> > > > > into
> > > > > a single thermal zone. Rename the thermal_zone_ops to
> > > > > thermal_sensor_ops, that will appear clearyl the thermal zone
> > > > > is
> > > > > not a
> > > > > sensor but an abstraction of one [or multiple] sensor(s).
> > > >
> > > > So I'm not convinced that the renaming mentioned above is
> > > > particularly
> > > > clean either.
> > > >
> > > > IMV the way to go would be to split the thermal sensor
> > > > operations,
> > > > like ->get_temp(), out of thermal_zone_ops.
> > > >
> > > > But then it is not clear what a thermal zone with multiple
> > > > sensors in
> > > > it really means.  I guess it would require an aggregation
> > > > function to
> > > > combine the thermal sensors in it that would produce an effective
> > > > temperature to check against the trip points.
> > > >
> > > > Honestly, I don't think that setting a separate set of trips for
> > > > each
> > > > sensor in a thermal zone would make a lot of sense.
> > >
>