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

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Date:   Wed, 07 Jun 2017 18:20:39 +0300
From:   Paul Kocialkowski <contact@...lk.fr>
To:     Pavel Machek <pavel@....cz>
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

Hey,

On Wed, 2017-06-07 at 09:52 +0200, Pavel Machek wrote:
> I'd pass to userspace what the controller reports. Yes, I seldom see
> > > > "STATUS_FULL" but that may be a problem we need to track down.
> > > 
> > > The controller is known, from my experience, to not be reliable in that
> > > regard,
> > > so I don't think it makes sense to pass a state that doesn't reflect the
> > > actual
> > > state of charging just because the chip tells us so.
> > > 
> > > Worst case, we could also have a dt property to enable that kind of fixup
> > > workaround and let every device maintainer decide whether it is relevant
> > > for
> > > their device.
> > 
> > Actually, since a similar fix[0] was accepted in sbs-battery, I'd rather not
> > make this optional but rather make it the default and perhaps have a dt prop
> > to
> > disable it.
> > 
> > [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.

> 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.

> 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;
> +	
-- 
Paul Kocialkowski, developer of free digital technology and hardware support

Website: https://www.paulk.fr/
Coding blog: https://code.paulk.fr/
Git repositories: https://git.paulk.fr/ https://git.code.paulk.fr/