Re: [PATCH v5 0/3] Thermal ACPI APIs for generic trip points

[Daniel Lezcano]

On 18/01/2023 22:16, srinivas pandruvada wrote:
> On Wed, 2023-01-18 at 22:01 +0100, Daniel Lezcano wrote:
> > On 18/01/2023 21:53, srinivas pandruvada wrote:
> > > On Wed, 2023-01-18 at 21:00 +0100, Daniel Lezcano wrote:
> > > > On 18/01/2023 20:16, srinivas pandruvada wrote:
> > > >
> > > > [ ... ]
> > > >
> > > > > > > But we'd better wait for the thermald test result from
> > > > > > > Srinvias.
> > > > > >
> > > > > > A quick test show that things still work with thermald and
> > > > > > these
> > > > > > changes.
> > > > >
> > > > > But I have a question. In some devices trip point temperature
> > > > > is
> > > > > not
> > > > > static. When hardware changes, we get notification. For example
> > > > > INT3403_PERF_TRIP_POINT_CHANGED for INT3403 drivers.
> > > > > Currently get_trip can get the latest changed value. But if we
> > > > > preregister, we need some mechanism to update them.
> > > >
> > > > When the notification INT3403_PERF_TRIP_POINT_CHANGED happens, we
> > > > call
> > > > int340x_thermal_read_trips() which in turn updates the trip
> > > > points.
> > >
> > > Not sure how we handle concurrency here when driver can freely
> > > update
> > > trips while thermal core is using trips.
> >
> > Don't we have the same race without this patch ? The thermal core can
> > call get_trip_temp() while there is an update, no ?
> Yes it is. But I can add a mutex locally here to solve.
> But not any longer.
>
> I think you need some thermal_zone_read_lock/unlock() in core, which
> can use rcu. Even mutex is fine as there will be no contention as
> updates to trips will be rare.

I was planning to provide a thermal_trips_update(tz, trips) and from 
there handle the locking.

As the race was already existing, can we postpone this change after the 
generic trip points changes?

There is still a lot of work to do to consolidate the code. One of them 
is to provide a generic function to browse the trip points and ensure 
the code is using it instead of directly inspect the thermal zone 
internals structure.

I'm almost there but I need the remaining Intel drivers changes to be 
merged (as well as ACPI which is finished but depending on this series).

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