linux-kernel - Re: [RFC] shutdown machine when li-ion battery goes below 3V

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Date:   Tue, 25 Oct 2016 12:53:20 +0200
From:   Pali Rohár <pali.rohar@...il.com>
To:     Pavel Machek <pavel@....cz>
Cc:     Tony Lindgren <tony@...mide.com>, sre@...nel.org,
        kernel list <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-omap@...r.kernel.org, khilman@...nel.org,
        aaro.koskinen@....fi, ivo.g.dimitrov.75@...il.com,
        patrikbachan@...il.com, serge@...lyn.com, abcloriens@...il.com
Subject: Re: [RFC] shutdown machine when li-ion battery goes below 3V

On Tuesday 25 October 2016 12:24:35 Pavel Machek wrote:
> On Mon 2016-10-24 23:48:47, Pali Rohár wrote:
> > On Monday 24 October 2016 23:41:52 Pavel Machek wrote:
> > > On Mon 2016-10-24 14:29:33, Tony Lindgren wrote:
> > > > Also, the shutdown voltage can depend on external devices
> > > > connected. It could be for example 3.3V depending on eMMC on some
> > > > devices while devices with no eMMC could have it at 3.0V.
> > > 
> > > Actually, I'd like to shutdown at 3.3V or more (like 3.5V), because
> > > going below that is pretty mean to the battery. But if I set
> > > threshold too high, GSM activity will push it below that for a very
> > > short while, and I'll shutdown too soon.
> > > 
> > > Ideas welcome...
> > 
> > bq27x00 has EDVF flag which means that battery is empty. Maemo with 
> > bq27x00 driver is configured to issue system shutdown when EDVF is set.
> > 
> > Maybe kernel should issue emergency shutdown e.g. after minute or two 
> > after EDVF flag is set?
> 
> Thanks for pointer.
> 
> EDVF seems to be exposed as health. ... but only if battery is
> calibrated, AFAICT.

No, EDVF is available also for uncalibrated battery. There are EDV1 and
EDVF flags. Both are set based on battery voltage and some other
parameters from bq EEPROM.

>  if (has_ci_flag && (cache.flags & BQ27000_FLAG_CI)) {
>       dev_info_once(di->dev, "battery is not calibrated! ignoring capacity values\n");

Yes, it ignores only capacity values (which needs calibration), not
those raw flags which works also without calibration.

>       ...
>       cache.health = -ENODATA;
> 
> Plus, it prioritizes battery cold over battery dead. IMO we don't need
> to shutdown on battery cold (we just may not charge the battery), but
> we need to shutdown on battery dead.
> 
> So something like this?
> 
> 								Pavel
> 
> Signed-off-by: Pavel Machek <pavel@....cz>
> 
> diff --git a/drivers/power/supply/bq27xxx_battery.c b/drivers/power/supply/bq27xxx_battery.c
> index 8eb2f8f..5ddf6d7 100644
> --- a/drivers/power/supply/bq27xxx_battery.c
> +++ b/drivers/power/supply/bq27xxx_battery.c
> @@ -680,10 +680,10 @@ static int bq27xxx_battery_read_health(struct bq27xxx_device_info *di)
>  	/* Unlikely but important to return first */
>  	if (unlikely(bq27xxx_battery_overtemp(di, flags)))
>  		return POWER_SUPPLY_HEALTH_OVERHEAT;
> -	if (unlikely(bq27xxx_battery_undertemp(di, flags)))
> -		return POWER_SUPPLY_HEALTH_COLD;
>  	if (unlikely(bq27xxx_battery_dead(di, flags)))
>  		return POWER_SUPPLY_HEALTH_DEAD;
> +	if (unlikely(bq27xxx_battery_undertemp(di, flags)))
> +		return POWER_SUPPLY_HEALTH_COLD;
>  
>  	return POWER_SUPPLY_HEALTH_GOOD;
>  }
> 
> 

Looks like this is OK.

-- 
Pali Rohár
pali.rohar@...il.com