linux-kernel - Re: [PATCH V2 2/2] power: twl4030_charger: attempt to power off in case of critical events

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Message-ID: <20140614222606.GB1389@xo-6d-61-c0.localdomain>
Date:	Sun, 15 Jun 2014 00:26:06 +0200
From:	Pavel Machek <pavel@....cz>
To:	Grazvydas Ignotas <notasas@...il.com>
Cc:	Nishanth Menon <nm@...com>, dbaryshkov@...il.com,
	Tony Lindgren <tony@...mide.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Felipe Balbi <balbi@...com>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	dwmw2@...radead.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH V2 2/2] power: twl4030_charger: attempt to power off in
 case of critical events

On Thu 2014-06-05 01:30:40, Grazvydas Ignotas wrote:
> On Wed, Jun 4, 2014 at 4:01 PM, Nishanth Menon <nm@...com> wrote:
> > On 06/04/2014 05:04 AM, Grazvydas Ignotas wrote:
> >> On Thu, May 29, 2014 at 12:46 AM, Nishanth Menon <nm@...com> wrote:
> >> often while charging on hot summer day. I'd prefer my pandora to not
> >> shutdown in such case, it could just stop charging instead.
> > Yeah, We could call
> >   twl4030_charger_enable_ac(false);
> >   twl4030_charger_enable_usb(bci, false);
> >
> > But then, is that sufficient?
> > From the TRM:
> > 7.5.8 Battery Temperature Out-of-Range Detection
> > Battery temperature out-of-range detection detects whether the battery
> > temperature is within a specific
> > range. Detection is possible for two temperature ranges. When the
> > battery temperature is not in the
> > 2???50°C range or is in the 3???43°C range, the TBATOR1 and TBATOR2 status
> > bits rise and an interrupt is
> > generated.
> > This MADC monitoring function can be enabled by writing to the
> > TBATOR1EN (BCIMFEN2[3]) and
> > TBATOR2EN (BCIMFEN2[1]) fields.
> >
> > Battery pack at high temperature is a risk, no? and it may not be just
> > charger that might be causing such a condition. Is'nt it safer to shut
> > the device down in such a case?
> 
> I don't know, so far nobody has complained about the battery exploding
> and anybody getting hurt, but it would make the device unusable for
> people in hot climates. From what I remember the automatic charge is
> stopped automatically on this condition, as some people complained
> they couldn't charge their device and saw these messages in dmesg. I
> guess mainline could choose the safer option and shutdown, no strong
> opinion about this.

Li-ions have strong casing -- battery will not explode, just will grow a bit. And
50C will probably not make it explode immediately, just shorten its life a lot.

If your battery is close enough to CPU (for example), it should be something else
that heats it up. I think that shutdown by default is a good idea.

If particular hardware triggers this a lot _and_ there are no components (CPU, hdd) 
heating the battery, you may want to just stop charging... but do it per-machine
...

Actually, you probably want to stop charging at 37C or so, to stop triggering this...

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