linux-kernel - Re: [PATCH 0/3] hwmon: (pmbus) add power from energy readings

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Date:   Wed, 6 Jul 2022 06:17:58 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     "Kallas, Pawel" <pawel.kallas@...el.com>
Cc:     jdelvare@...e.com, corbet@....net, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        iwona.winiarska@...el.com
Subject: Re: [PATCH 0/3] hwmon: (pmbus) add power from energy readings

On Wed, Jul 06, 2022 at 12:40:21PM +0200, Kallas, Pawel wrote:
> Add support for reading EIN or EOUT registers and expose power calculated
> from energy. This is more accurate than PIN and POUT power readings.
> Readings are exposed in new hwmon files power1_average and power2_average.
> Also add support for QUERY command that is needed to check availability
> of EIN and EOUT reads and its data format. Only direct data format is
> supported due to lack of test devices supporting other formats.
> 

I don't think this is a good idea. EIN/EOUT report energy consumption,
not power. The "average" attributes as implemented don't really report
a reliable number since the averaging period is not defined. Also, kernel
drivers should not make up such numbers. I don't mind adding energy
attribute support, but that should be reported as what it is, energy.
What userspace does with it would then be a userspace concern; it can
calculate all kinds of averages from it as much as it wants.

Also, new attributes should not depend on query command support.
I don't mind adding support for that, but it would have to be independent
of energy attribute support.

Thanks,
Guenter

> Kallas, Pawel (3):
>   hwmon: (pmbus) add support for QUERY command
>   hwmon: (pmbus) refactor sensor initialization
>   hwmon: (pmbus) add EIN and EOUT readings
> 
>  Documentation/hwmon/pmbus-core.rst |   7 +
>  drivers/hwmon/pmbus/pmbus.c        |  20 +++
>  drivers/hwmon/pmbus/pmbus.h        |  19 +++
>  drivers/hwmon/pmbus/pmbus_core.c   | 261 +++++++++++++++++++++++++++--
>  4 files changed, 291 insertions(+), 16 deletions(-)
> 
> 
> base-commit: 7c1de25c06f31b04744beae891baf147af9ba0cb