linux-kernel - Re: [PATCH 5/5] power: supply: bq27xxx: Correct supply status with current draw

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Message-ID: <20170607195023.GA4083@amd>
Date:   Wed, 7 Jun 2017 21:50:23 +0200
From:   Pavel Machek <pavel@....cz>
To:     Paul Kocialkowski <contact@...lk.fr>
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Pali Rohár <pali.rohar@...il.com>,
        "Andrew F . Davis" <afd@...com>,
        Sebastian Reichel <sre@...nel.org>,
        Chris Lapa <chris@...a.com.au>,
        Matt Ranostay <mranostay@...il.com>
Subject: Re: [PATCH 5/5] power: supply: bq27xxx: Correct supply status with
 current draw

Hi!

> On Wed, 2017-06-07 at 09:52 +0200, Pavel Machek wrote:
> > > [0]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/comm
> > > it/?
> > > h=v4.12-rc4&id=7f93e1fa032bb5ee19b868b9649bc98c82553003
> > 
> > Is there some documentation that explains what different power supply
> > statuses mean? Because without that, we can have long and useless
> > discussions.
> 
> Well, I couldn't really find much except the following from Documentation/
> (which is not that helpful, and the BATTERY_STATUS_* don't seem to exist
> anymore):
> 
> " STATUS - this attribute represents operating status (charging, full,
> discharging (i.e. powering a load), etc.). This corresponds to
> BATTERY_STATUS_* values, as defined in battery.h. "
> 
> Generally speaking, I think the question to be asked is what information users
> will be interested in in each scenario we have to consider.

Hmm. We really should add some documentation :-(.

> > If you have 40Wh battery, and you are charging it with 1mW, I don't
> > believe you should be indicating "charging". That battery is
> > full. Yes, even full batteries are sometimes charged with very low
> > currents to keep them full.
> 
> That makes sense. Note that this patch was however designed to solve the problem
> the other way round: my device will report full battery when the PSU was
> disconnected and that it is, in fact, drawing significant current.

That is documented / correct behaviour sometimes. Thinkpad batteries
have thresholds -- lets say 100% and 95%. They charge battery to full
(as expected), but then they won't start charging battery again unless
it drops below 95%. So you can have "battery full, charger
disconnected" state.

[Design like this prolongs longevity of li-ion batteries.]

> > And I'm not sure what this is supposed to do, but its quite strange
> > code.
> 
> Could you comment on what is strange about it? This function corrects the status
> based on the current flow as explained through this thread.
> 
> > +static int sbs_status_correct(struct i2c_client *client, int *intval)
> > +{
> > +	int ret;
> > +
> > +	ret = sbs_read_word_data(client, sbs_data[REG_CURRENT].addr);
> > +	if (ret < 0)
> > +	   return ret;
> > +
> > +	ret = (s16)ret;

The last line ... is strange.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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