linux-kernel - Re: [PATCH v4 2/4] power: supply: core: add input voltage/current measurements

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Message-ID: <20200502224526.GA25127@qmqm.qmqm.pl>
Date:   Sun, 3 May 2020 00:45:26 +0200
From:   Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:     Sebastian Reichel <sebastian.reichel@...labora.com>
Cc:     clang-built-linux@...glegroups.com, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH v4 2/4] power: supply: core: add input voltage/current
 measurements

On Sun, May 03, 2020 at 12:23:49AM +0200, Sebastian Reichel wrote:
> Hi,
> 
> On Fri, May 01, 2020 at 05:11:18PM +0200, Michał Mirosław wrote:
> > Introduce input voltage and current limits and measurements.
> > This makes room for e.g. VBUS measurements in USB chargers.
> We already have properties for charger input voltage/current.
> Unfortunately the naming is not as straight forward, as it
> could be. Basically the properties have been added over time
> and are ABI now. Things are documented in
> 
> Documentation/ABI/testing/sysfs-class-power
> 
> I provided the relevant properties below.

Hmm. Looks like there is no battery current/voltage properties then?
This is different from IBUS (input current), as IBUS = charging
current + system load. Documentation/power/power_supply_class.rst is
missing descriptions for the properties you mention.

[...]
> > --- a/include/linux/power_supply.h
> > +++ b/include/linux/power_supply.h
> > @@ -127,7 +127,9 @@ enum power_supply_property {
> >  	POWER_SUPPLY_PROP_CHARGE_CONTROL_LIMIT_MAX,
> >  	POWER_SUPPLY_PROP_CHARGE_CONTROL_START_THRESHOLD, /* in percents! */
> >  	POWER_SUPPLY_PROP_CHARGE_CONTROL_END_THRESHOLD, /* in percents! */
> > +	POWER_SUPPLY_PROP_INPUT_CURRENT_NOW,
> 
> What:           /sys/class/power_supply/<supply_name>/current_avg    
> Date:           May 2007
> Contact:        linux-pm@...r.kernel.org                          
> Description:                  
>                 Reports an average IBUS current reading over a fixed period.   
>                 Normally devices will provide a fixed interval in which they   
>                 average readings to smooth out the reported value.             
>                                                                                 
>                 Access: Read    
>                 Valid values: Represented in microamps
> 

There are two entries for /sys/class/power_supply/<supply_name>/current_avg
in the file, the other one mentions IBAT instead. "voltage_now" has the
same problem. There seems to be a split-personality disorder present in
the kernel ABI. ;-)

Best Regards,
Michał Mirosław