linux-kernel - Re: [PATCH 1/2] thermal: core: add initial support for cold and critical

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Message-ID: <CAJZ5v0iBx3+BY8960C-GG2EdfUdt_E_o4KjKZ5gmx_f73BJGuQ@mail.gmail.com>
Date:   Wed, 13 Dec 2023 15:39:54 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Christian Marangi <ansuelsmth@...il.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Lukasz Luba <lukasz.luba@....com>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] thermal: core: add initial support for cold and
 critical_cold trip point

On Wed, Dec 13, 2023 at 1:06 PM Christian Marangi <ansuelsmth@...il.com> wrote:
>
> On Wed, Dec 13, 2023 at 01:01:51PM +0100, Rafael J. Wysocki wrote:
> > On Tue, Dec 12, 2023 at 11:17 PM Christian Marangi <ansuelsmth@...il.com> wrote:
> > >
> > > Add initial support for cold and critical_cold trip point. Many if not
> > > all hwmon and thermal device have normally trip point for hot
> > > temperature and for cold temperature.
> > >
> > > Till now only hot temperature were supported. Add support for also cold
> > > temperature to permit complete definition of cold trip point in DT.
> > >
> > > Thermal driver may use these additional trip point to correctly set
> > > interrupt for cold temperature values and react based on that with
> > > various measure like enabling attached heater, forcing higher voltage
> > > and other specialaized peripherals.
> > >
> > > For hwmon drivers this is needed as currently there is a problem with
> > > setting the full operating range of the device for thermal devices
> > > defined with hwmon. To better describe the problem, the following
> > > example is needed:
> > >
> > > In the scenario of a simple hwmon with an active trip point declared
> > > and a cooling device attached, the hwmon subsystem currently set the
> > > min and max trip point based on the single active trip point.
> > > Thermal subsystem parse all the trip points and calculate the lowest and
> > > the highest trip point and calls the .set_trip of hwmon to setup the
> > > trip points.
> > >
> > > The fact that we currently don't have a way to declare the cold/min
> > > temperature values, makes the thermal subsystem to set the low value as
> > > -INT_MAX.
> > > For hwmon drivers that doesn't use clamp_value and actually reject
> > > invalid values for the trip point, this results in the hwmon settings to
> > > be rejected.
> > >
> > > To permit to pass the correct range of trip point, permit to set in DT
> > > also cold and critical_cold trip point.
> > >
> > > Thermal driver may also define .cold and .critical_cold to act on these
> > > trip point tripped and apply the required measure.
> > >
> > > Signed-off-by: Christian Marangi <ansuelsmth@...il.com>
> >
> > Generally speaking, it is kind of late in the cycle for adding
> > significant new features like this.  We can get to it when 6.8-rc1 is
> > out, so please resend then.
> >
>
> Ok no problem.
>
> > Also it would be nice to define/document the cold and crtitical_cold
> > trip points somewhere and is there a better name for critical_cold?
> >
>
> Ehhh I think critical_cold is the only correct one.
> Thermal device normally have lowest low high and highest trip point. I
> think the lowest has to match what we use for highest (critical). Using
> coldest might be confusing and wouldn't display a critical condition of
> low temp where the device can't work and immediate actions has to be
> taken.

So at least make it shorter, like crit_cold?