linux-kernel - Re: [PATCH v2 2/3] bq2415x_charger: Use power

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Message-ID: <1434978251.31721.1385404366021.JavaMail.apache@mail83.abv.bg>
Date:	Mon, 25 Nov 2013 20:32:46 +0200 (EET)
From:	Ивайло Димитров 
	<freemangordon@....bg>
To:	Sebastian Reichel <sre@...g0.de>
Cc:	pavel@....cz, pali.rohar@...il.com, anton@...msg.org,
	dwmw2@...radead.org, tony@...mide.com, linux@....linux.org.uk,
	linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
	aaro.koskinen@....fi
Subject: Re: [PATCH v2 2/3] bq2415x_charger: Use power_supply notifier for automode

  >-------- Оригинално писмо --------
 >От:  Sebastian Reichel 
 >Относно: Re: [PATCH v2 2/3] bq2415x_charger: Use power_supply notifier for
 automode
 >До: Ивайло Димитров 
 >Изпратено на: Понеделник, 2013, Ноември 25 19:14:21 EET
 >
 >
 >On Mon, Nov 25, 2013 at 07:01:54PM +0200, Ивайло Димитров wrote:
 >>> Now.. Imagine phone left in car in charger (on sun). Likely
 >>> temperature will reach high values, kernel is charging, dsme will
 >>> reboot the system, but kernel will start charging again, dsme will
 >>> reboot again, ...
 >>>
 >>> And it is not only high temperatures that are problem for li-ion
 >>> charging; battery should not be fast charged below 5C and should not
 >>> be charged below 0C. (Again, both are likely to happen if you leave
 >>> your phone in car).
 >>>
 >>> AFAICT, we should simply disable charging below 5C or above 45C.
 >> 
 >> AFAIK dsme will not restart it, but power it off, so the above
 >> scenario won't happen.
 >
 >Just assume what happens, when dsme does not start (e.g. system boot
 >hangs).
 >
 >If everything is controlled from userspace, charger would not start
 >(-> safe!). If everything is controlled by the kernel, temperature
 >safety checks are taken (-> safe!). But in the currently proposed
 >variant: No safety checks.
 >
 >-- Sebastian
 >
 >

Hmm, you have a point here :)

So, AIUI there are 2 options:

1. charger driver polls the battery driver every n (60?) seconds.
2. battery driver sends PSY_EVENT_PROP_CHANGED on every degree up or
down
 
In both cases if the temperature is outside of the safe margins, the
charging should be stopped.

2 seems more generic to me, but as rx51-battery is missing the
functionality to send events on temperature change, I guess 1 will
be easier to implement.

And I think there should be some method (sysfs entry?, /dev/bqxxx
opened?) to tell the charger driver to stop polling the battery 
driver once (and if) the userspace has started to take care of the 
battery temperature - makes no sense to duplicate the checks IMO.

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