linux-kernel - Re: [PATCH] battery: Fix charge_now returned by broken batteries

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Message-ID: <ca2dc2820910041046i47a1c3dhba82266bb14a440c@mail.gmail.com>
Date:	Sun, 4 Oct 2009 19:46:42 +0200
From:	Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
Cc:	astarikovskiy@...e.de, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] battery: Fix charge_now returned by broken batteries

On Sun, Oct 4, 2009 at 6:45 PM, Henrique de Moraes Holschuh
<hmh@....eng.br> wrote:
> On Sun, 04 Oct 2009, Miguel Ojeda wrote:
>> Some broken batteries like my DELL NR2227 or a friend's DELL GK4798 return
>> the design_capacity (charge_full_design) as capacity_now (charge_now)
>> when completely charged.
>>
>> I noticed this when looking at a battery plugin that reported "127% charged".
>> Some of these plugins have already "fixed" this in userspace by coding
>> something like min(percentage, 100)).
>
> A battery can be charged above 100%.  It just depends what you call 100%,
> and the "I am full" level *varies* in a non-monotonic way during the battery
> lifetime...
>
> So, if you don't want to see > 100%, you have to clamp it to 100% and lose
> information (when your "100%" level is actually increasing as the thing
> keeps charging and you keep raising the baseline so that it doesn't go over
> 100%).

If the 100% level increased, then full_charge_capacity (a.k.a. "_last_
full capacity" as seen in /proc) will increase as well, won't it? If
the battery went over that 100% that means there is a "new" 100%, why
are we losing information?.

I am asking, I am not an expert on battery stuff.

>
>> So I discovered that the battery wrongly returns charge_full_design when
>> completely charged instead of charge_full.
>
> Ick.
>
>> This patch fixes this by returning min(capacity_now, full_charge_capacity)
>> on both procfs and sysfs.
>
> What will it cause on non-broken batteries?  Or during gauge reset, when any
> battery that updates full_charge_capacity only at the end of the cycle will
> really have capacity_now > full_charge_capacity ?

Well, does it make sense to have capacity_now higher than
full_charge_capacity? Wouldn't that information be broken too?

Again, I am just wondering.

>
>> Now the userspace plugins report the correct 100% and their userspace check
>> may not be needed (if this error is the only one producing >100% results).
>
> Like I said, > 100% can happen, unless what you define to be 100% is very
> elastic (and gets updated all the time).

I still think it does not make sense to have a battery charged over
its 100% capacity whatever the definition of 100% is. Maybe I do not
understand your point.

>
> --
>  "One disk to rule them all, One disk to find them. One disk to bring
>  them all and in the darkness grind them. In the Land of Redmond
>  where the shadows lie." -- The Silicon Valley Tarot
>  Henrique Holschuh
>
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