linux-kernel - Re: [PATCH v2 1/8] add header file for kelvin to/from Celsius conversion helpers

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Date:   Sun, 8 Dec 2019 00:57:28 +0900
From:   Akinobu Mita <akinobu.mita@...il.com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     Linux NVMe Mailinglist <linux-nvme@...ts.infradead.org>,
        linux-hwmon@...r.kernel.org, Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Sujith Thomas <sujith.thomas@...el.com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Amit Kucheria <amit.kucheria@...durent.com>,
        Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>
Subject: Re: [PATCH v2 1/8] add header file for kelvin to/from Celsius
 conversion helpers

2019年12月7日(土) 1:49 Daniel Lezcano <daniel.lezcano@...aro.org>:
>
> On 28/11/2019 15:54, Akinobu Mita wrote:
> > There are several helper macros to convert kelvin to/from Celsius in
> > <linux/thermal.h> for thermal drivers.  These are useful for any other
> > drivers or subsystems, but it's odd to include <linux/thermal.h> just for
> > the helpers.
> >
> > This adds a new <linux/temperature.h> that provides the equivalent inline
> > functions for any drivers or subsystems.  It is intended to replace the
> > helpers in <linux/thermal.h>.
> >
> > Cc: Sujith Thomas <sujith.thomas@...el.com>
> > Cc: Darren Hart <dvhart@...radead.org>
> > Cc: Andy Shevchenko <andy@...radead.org>
> > Cc: Zhang Rui <rui.zhang@...el.com>
> > Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
> > Cc: Amit Kucheria <amit.kucheria@...durent.com>
> > Cc: Jean Delvare <jdelvare@...e.com>
> > Cc: Guenter Roeck <linux@...ck-us.net>
> > Cc: Keith Busch <kbusch@...nel.org>
> > Cc: Jens Axboe <axboe@...com>
> > Cc: Christoph Hellwig <hch@....de>
> > Cc: Sagi Grimberg <sagi@...mberg.me>
> > Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
> > ---
> > * v2
> > - add deci_kelvin_to_millicelsius_with_offset() in linux/temperature.h
> > - stop including linux/temperature.h from linux/thermal.h
> >
> >  include/linux/temperature.h | 51 +++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 51 insertions(+)
> >  create mode 100644 include/linux/temperature.h
> >
> > diff --git a/include/linux/temperature.h b/include/linux/temperature.h
> > new file mode 100644
> > index 0000000..679e70a
> > --- /dev/null
> > +++ b/include/linux/temperature.h
> > @@ -0,0 +1,51 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef _LINUX_TEMPERATURE_H
> > +#define _LINUX_TEMPERATURE_H
>
> It sounds strange to create a temperature file just for a few conversion
> functions. Why not create an units.h file, so some more conversions
> could be added later (not necessarily related to temperature) ?

Fine with me.

> > +#include <linux/kernel.h>
> > +
> > +#define ABSOLUTE_ZERO_MILLICELSIUS -273150
> > +
> > +static inline long kelvin_to_millicelsius(long t)
>
> Why 'long' ?

There's no specific reason, but the existing DECI_KELVIN_TO_CELSIUS() in
linux/thermal.h converts to 'long'.

Do you prefer changing 'long' to 'int'?

> > +{
> > +     return t * 1000 + ABSOLUTE_ZERO_MILLICELSIUS;
> > +}
> > +
> > +static inline long millicelsius_to_kelvin(long t)
> > +{
> > +     return DIV_ROUND_CLOSEST(t - ABSOLUTE_ZERO_MILLICELSIUS, 1000);
>
> Please don't duplicate these operations, just do the conversion to the
> right unit and then call a single function.
>
> Replace the constant by macros like what we find in time64.h.
>
> eg.
> #define MILLICELSIUS_PER_CELCIUS 1000

How about this?

#define ABSOLUTE_ZERO_MILLICELSIUS -273150

static inline long milli_kelvin_to_millicelsius(long t)
{
        return t + ABSOLUTE_ZERO_MILLICELSIUS;
}

static inline long millicelsius_to_milli_kelvin(long t)
{
        return t - ABSOLUTE_ZERO_MILLICELSIUS;
}

#define MILLIDEGREE_PER_DEGREE 1000
#define MILLIDEGREE_PER_DECIDEGREE 100

static inline long kelvin_to_millicelsius(long t)
{
        return milli_kelvin_to_millicelsius(t * MILLIDEGREE_PER_DEGREE);
}

static inline long millicelsius_to_kelvin(long t)
{
        t = millicelsius_to_milli_kelvin(t);

        return DIV_ROUND_CLOSEST(t, MILLIDEGREE_PER_DEGREE);
}

static inline long deci_kelvin_to_celsius(long t)
{
        t = milli_kelvin_to_millicelsius(t * MILLIDEGREE_PER_DECIDEGREE);

        return DIV_ROUND_CLOSEST(t, MILLIDEGREE_PER_DEGREE);
}

static inline long celsius_to_deci_kelvin(long t)
{
        t = millicelsius_to_milli_kelvin(t * MILLIDEGREE_PER_DEGREE);

        return DIV_ROUND_CLOSEST(t, MILLIDEGREE_PER_DECIDEGREE);
}

/**
 * deci_kelvin_to_millicelsius_with_offset - convert Kelvin to Celsius
 * @t: temperature value in decidegrees Kelvin
 * @offset: difference between Kelvin and Celsius in millidegrees
 *
 * Return: temperature value in millidegrees Celsius
 */
static inline long deci_kelvin_to_millicelsius_with_offset(long t, long offset)
{
        return t * MILLIDEGREE_PER_DECIDEGREE - offset;
}

static inline long deci_kelvin_to_millicelsius(long t)
{
        return milli_kelvin_to_millicelsius(t * MILLIDEGREE_PER_DECIDEGREE);
}

static inline long millicelsius_to_deci_kelvin(long t)
{
        t = millicelsius_to_milli_kelvin(t);

        return DIV_ROUND_CLOSEST(t, MILLIDEGREE_PER_DECIDEGREE);
}

> So you can really do the cleanup in all the drivers, like removing:

OK.  I'll try as much as possible.