linux-kernel - Re: [Kernel-discuss] Re: [PATCH 3/7] [RFC] Battery monitoring class

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Date:	Fri, 13 Apr 2007 00:44:13 +0400
From:	Anton Vorontsov <cbou@...l.ru>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
Cc:	Paul Sokolovsky <pmiscml@...il.com>,
	Matthew Garrett <mjg59@...f.ucam.org>, dwmw2@...radead.org,
	linux-kernel@...r.kernel.org, kernel-discuss@...dhelds.org,
	Shem Multinymous <multinymous@...il.com>
Subject: Re: [Kernel-discuss] Re: [PATCH 3/7] [RFC] Battery monitoring class

On Thu, Apr 12, 2007 at 03:56:30PM -0300, Henrique de Moraes Holschuh wrote:
> On Thu, 12 Apr 2007, Paul Sokolovsky wrote:
> >   Yes, that's apparently the way to go. We just should consider
> > if mAh and mWh are enough, or we go wider and allow whole collection of
> > units. Btw, original handhelds.org code used Joules ;-).
> 
> FWIW, SBS only mentions mAh and mWh.  AFAIK, all other (meaningful) units
> should be able to be converted to either Ah or Wh, assuming enough precision
> on the math.  I never heard of any other way to fuel-gauge batteries than
> these two main modes (current-based or capacity-based), but I don't work on
> the battery field.

Okay, I have an idea:

Let's name attributes with mWh units as {min_,max_,design_,}energy,
and attributes with mAh units as {min_,max_,design_,}charge.

Because both energy and charge represents ""capacity"" in some meanings,
and that's why we bothering with _units attribute. So, lets drop
"capacity"* and use more specific terms? I really don't want string
attributes by default (except status).

If we export attributes with predefined units, userspace developers
could just look into include/linux/battery.h and conclude: "Ah, great,
if battery reporting energy, then it's in mWh, and if battery reporting
charge it's always in mAh".

* Yup, I've read last discussion regarding batteries, and I've seen
  objections against "charge" term, quoting Shem Multinymous:

  "And, for the reasons I explained earlier, I strongly suggest not using
  the term "charge" except when referring to the action of charging.
  Hence:
  s/charge_rate/rate/;  s/charge/capacity/"

  But lets think about it once again? We'll make things much cleaner
  if we'll drop "capacity" at all.

> That said, you may need to use uWh and uAh instead of mAh and mWh, though.

Not sure. Is there any existing chip that can report uAh/uWh? That is
great precision.

-- 
Anton Vorontsov
email: cbou@...l.ru
backup email: ya-cbou@...dex.ru
irc://irc.freenode.org/bd2
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