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

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Date:	Thu, 28 Nov 2013 01:25:50 +0100
From:	Sebastian Reichel <sre@...ian.org>
To:	Pali Rohár <pali.rohar@...il.com>
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 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

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