linux-kernel - Re: [PATCH v5 1/3] thermal/acpi: Add ACPI trip point routines

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Date:   Fri, 20 Jan 2023 19:15:22 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        srinivas.pandruvada@...ux.intel.com, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        rui.zhang@...el.com, christophe.jaillet@...adoo.fr
Subject: Re: [PATCH v5 1/3] thermal/acpi: Add ACPI trip point routines

On Fri, Jan 20, 2023 at 7:08 PM Daniel Lezcano
<daniel.lezcano@...aro.org> wrote:
>
>
> Hi Rafael,
>
>
> On 19/01/2023 14:15, Rafael J. Wysocki wrote:
>
> [ ... ]
>
> >> +static int thermal_acpi_get_temperature_object(struct acpi_device *adev,
> >> +                                              char *object, int *temperature)
> >
> > So this would become thermal_acpi_get_temp_object(). or even
> > thermal_acpi_get_temp() because it really returns the temperature
> > value.
> >
> > I also don't particularly like returning values via pointers, which is
> > entirely avoidable here, because the temperature value obtained from
> > the ACPI control methods must be a positive number.
> >
> > So I would make it
> >
> > static int thermal_acpi_get_temp(struct acpi_device *adev, char *object_name)
> > {
>
> We are converting decikelvin -> millicelsius. Even it is very unlikely,
> the result could be less than zero (eg. -1°C). We won't be able to
> differentiate -ENODATA with a negative value, no ?
>
> In the future, it is possible we will have to deal with cold trip points
> in order to warm a board. May be we should don't care for now ?

My point is that the ACPI specification mandates that the return
values be in deciK and so always non-negative.