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

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Message-Id: <201311280753.11274@pali>
Date:	Thu, 28 Nov 2013 07:53:10 +0100
From:	Pali Rohár <pali.rohar@...il.com>
To:	Sebastian Reichel <sre@...ian.org>
Cc:	Ивайло Димитров 
	<freemangordon@....bg>, pavel@....cz, 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

On Thursday 28 November 2013 01:25:50 Sebastian Reichel wrote:
> On Wed, Nov 27, 2013 at 10:16:47PM +0100, Pali Rohár wrote:
> > On Monday 25 November 2013 22:50:01 Sebastian Reichel wrote:
> > > > 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.
> > > 
> > > The temperature must be polled anyway, if the ADC does not
> > > support interrupts.
> > 
> > Yes, ADC does not support interrupts, temperature must be
> > polled. Also bq27200 chip does not support interrupts, but
> > bq27x00_battery driver using delayed work which every 60s
> > poll all values (timeout can be configured via modprobe
> > param). So similar code can be added to rx51_battery.ko
> > too.
> 
> I think the safest implementation would be:
> 
> bq2415x polls the temperature from rx51-battery in the bq2415x
> watchdog handler. That way discontinuation of the charge
> process is guaranteed.
> 
> To avoid useless ADC conversion the rx51-battery driver caches
> the converted temperature value for a reasonable time (e.g.
> 10 seconds). This helps if multiple users want to read the
> battery temperature (e.g. userspace).
> 
> This also means, that the kernel stuff can handle charging
> autonomously and the userland daemon checks the battery
> temperature only for emergency shutdown (I guess the
> temperatures for stopping the charging and emergency shutdown
> are different).
> 
> IMHO it makes sense to move the emergency shutdown also into
> the kernel (but different driver!) in the future, but that's
> another topic :)
> 
> -- Sebastian

Just to note, here is original nokia table of temperature limits:

https://gitorious.org/rx51-bme-replacement/dsme-thermalobject-surface/source/master:modules/thermalobject_surface.c#L40

-- 
Pali Rohár
pali.rohar@...il.com

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