Date:   Fri, 6 Dec 2019 17:49:18 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Akinobu Mita <akinobu.mita@...il.com>,
        linux-nvme@...ts.infradead.org, linux-hwmon@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     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

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) ?

> +#include <linux/kernel.h>
> +
> +#define ABSOLUTE_ZERO_MILLICELSIUS -273150
> +
> +static inline long kelvin_to_millicelsius(long t)

Why 'long' ?

> +{
> +	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

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

drivers/iio/adc/qcom-vadc-common.h:#define KELVINMIL_CELSIUSMIL
        273150
drivers/iio/pressure/st_pressure_core.c:#define MCELSIUS_PER_CELSIUS
                1000
drivers/hwmon/xgene-hwmon.c:#define CELSIUS_TO_mCELSIUS(x)
((x) * 1000)
drivers/net/wireless/intel/iwlegacy/common.h:#define
KELVIN_TO_CELSIUS(x) ((x)-273)
drivers/net/wireless/intel/iwlegacy/common.h:#define
CELSIUS_TO_KELVIN(x) ((x)+273)
drivers/net/wireless/intel/iwlwifi/dvm/dev.h:#define
KELVIN_TO_CELSIUS(x) ((x)-273)
drivers/net/wireless/intel/iwlwifi/dvm/dev.h:#define
CELSIUS_TO_KELVIN(x) ((x)+273)
drivers/power/supply/sbs-battery.c:#define TEMP_KELVIN_TO_CELSIUS
        2731
drivers/thermal/armada_thermal.c:#define TO_MCELSIUS(c)
((c) * 1000)
drivers/thermal/rcar_gen3_thermal.c:#define MCELSIUS(temp)      ((temp)
* 1000)
drivers/thermal/rcar_thermal.c:#define MCELSIUS(temp)
((temp) * 1000)
drivers/thermal/samsung/exynos_tmu.c:#define MCELSIUS   1000
drivers/thermal/samsung/exynos_tmu.c:                   temp /= MCELSIUS;
drivers/thermal/samsung/exynos_tmu.c:                   hyst /= MCELSIUS;
drivers/thermal/samsung/exynos_tmu.c:   ref = trips[0].temperature /
MCELSIUS;
drivers/thermal/samsung/exynos_tmu.c:           *temp =
code_to_temp(data, value) * MCELSIUS;
drivers/thermal/samsung/exynos_tmu.c:           temp /= MCELSIUS;


> +}
> +
> +static inline long deci_kelvin_to_celsius(long t)
> +{
> +	return DIV_ROUND_CLOSEST(t * 100 + ABSOLUTE_ZERO_MILLICELSIUS, 1000);
> +}
> +
> +static inline long celsius_to_deci_kelvin(long t)
> +{
> +	return t * 10 - DIV_ROUND_CLOSEST(ABSOLUTE_ZERO_MILLICELSIUS, 100);
> +}
> +
> +/**
> + * 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 * 100 - offset;
> +}
> +
> +static inline long deci_kelvin_to_millicelsius(long t)
> +{
> +	return t * 100 + ABSOLUTE_ZERO_MILLICELSIUS;
> +}
> +
> +static inline long millicelsius_to_deci_kelvin(long t)
> +{
> +	return DIV_ROUND_CLOSEST(t - ABSOLUTE_ZERO_MILLICELSIUS, 100);
> +}
> +
> +#endif /* _LINUX_TEMPERATURE_H */
> 


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