linux-kernel - Re: [PATCH] bq27x00_battery: Fix reporting battery temperature

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Date:	Wed, 6 Feb 2013 18:56:34 +0100
From:	Pali Rohár <pali.rohar@...il.com>
To:	Anton Vorontsov <anton@...msg.org>
Cc:	David Woodhouse <dwmw2@...radead.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bq27x00_battery: Fix reporting battery temperature

On Sunday 03 February 2013 21:05:57 Anton Vorontsov wrote:
> On Sun, Feb 03, 2013 at 09:01:54PM +0100, Pali Rohár wrote:
> > On Sunday 03 February 2013 04:44:51 Anton Vorontsov wrote:
> > > On Sat, Feb 02, 2013 at 11:06:09AM +0100, Pali Rohár wrote:
> > > > Reported temperature can be also negative, so cache
> > > > value in non negative Kelvin degree.
> > > > 
> > > > Signed-off-by: Pali Rohár <pali.rohar@...il.com>
> > > > ---
> > > 
> > > Applied, thanks!
> > 
> > Now I looked at bq27x00_battery and rx51_battery drivers and
> > I see that both drivers reporting temperature in different
> > units. bq27x00_battery in 1/10 °C and rx51_battery in 1/100
> > °C. What is correct degree for kernel power power supply
> > API? Maybe other kernel drivers have different units too...
> > Note that my above patch did not changed anything units,
> > only fixed reporting (possible) negative temperature.
> 
> Per Documentation/power/power_supply_class.txt and
> power_supply.h:
> 
> /*
>  * All voltages, currents, charges, energies, time and
> temperatures in uV, * µA, µAh, µWh, seconds and tenths of
> degree Celsius unless otherwise * stated. It's driver's job
> to convert its raw values to units in which * this class
> operates.
>  */
> 
> Feel free to fix the offending drivers.
> 
> Thanks,
> 
> Anton

Ok, here is small patch which fixing it in bq27x00_battery driver.
Tested on Nokia N900 with patched 3.8-rc3 kernel.
bq27x00_battery reporting "POWER_SUPPLY_TEMP=2700"
and rx51_battery reporting "POWER_SUPPLY_TEMP=3590"

From 43a99615d6d7375770736303f1e000f3d85d75cb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pali=20Roh=C3=A1r?= <pali.rohar@...il.com>
Date: Sun, 3 Feb 2013 22:06:20 +0100
Subject: [PATCH] bq27x00_battery: Report temperature in 1/100 degree Celsius
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

* Documentation/power/power_supply_class.txt say that temperature must be reported in tenths of degree 
Celsius

Signed-off-by: Pali Rohár <pali.rohar@...il.com>
---
 drivers/power/bq27x00_battery.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/power/bq27x00_battery.c b/drivers/power/bq27x00_battery.c
index 5b077af..482755f 100644
--- a/drivers/power/bq27x00_battery.c
+++ b/drivers/power/bq27x00_battery.c
@@ -312,8 +312,10 @@ static int bq27x00_battery_read_temperature(struct bq27x00_device_info *di)
 		return temp;
 	}
 
-	if (!bq27xxx_is_chip_version_higher(di))
-		temp = 5 * temp / 2;
+	if (bq27xxx_is_chip_version_higher(di))
+		temp *= 10;
+	else
+		temp *= 25;
 
 	return temp;
 }
@@ -640,7 +642,7 @@ static int bq27x00_battery_get_property(struct power_supply *psy,
 	case POWER_SUPPLY_PROP_TEMP:
 		ret = bq27x00_simple_value(di->cache.temperature, val);
 		if (ret == 0)
-			val->intval -= 2731;
+			val->intval -= 27310;
 		break;
 	case POWER_SUPPLY_PROP_TIME_TO_EMPTY_NOW:
 		ret = bq27x00_simple_value(di->cache.time_to_empty, val);
-- 
1.7.10.4

-- 
Pali Rohár
pali.rohar@...il.com

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