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

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Message-ID: <b51ecbb8ac774efc4fb4ac1349585b486303f86f.camel@linux.intel.com>
Date:   Wed, 18 Jan 2023 15:04:44 -0800
From:   srinivas pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        "Zhang, Rui" <rui.zhang@...el.com>,
        "rafael@...nel.org" <rafael@...nel.org>
Cc:     "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "christophe.jaillet@...adoo.fr" <christophe.jaillet@...adoo.fr>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v5 0/3] Thermal ACPI APIs for generic trip points

On Wed, 2023-01-18 at 23:14 +0100, Daniel Lezcano wrote:
> 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?
I think so.

> 
> 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).
> 
Sounds good.

You can add my tested by for this.

Thanks,
Srinivas