linux-kernel - Re: [PATCH 01/15] power: supply: olpc_battery: correct the temperature units

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Date:   Sun, 21 Oct 2018 23:27:37 +0200
From:   Sebastian Reichel <sre@...nel.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Lubomir Rintel <lkundrak@...sk>,
        David Woodhouse <dwmw2@...radead.org>,
        Mark Brown <broonie@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        quozl@...top.org, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Eric Miao <eric.y.miao@...il.com>,
        Haojian Zhuang <haojian.zhuang@...il.com>,
        Daniel Mack <daniel@...que.org>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        linux-spi <linux-spi@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        devel@...verdev.osuosl.org, Linux PM <linux-pm@...r.kernel.org>,
        Stable <stable@...r.kernel.org>
Subject: Re: [PATCH 01/15] power: supply: olpc_battery: correct the
 temperature units

Hi,

On Fri, Oct 19, 2018 at 04:00:32PM +0300, Andy Shevchenko wrote:
> On Wed, Oct 10, 2018 at 8:23 PM Lubomir Rintel <lkundrak@...sk> wrote:
> >
> > According to [1] and [2], the temperature values are in tenths of degree
> > Celsius. Exposing the Celsius value makes the battery appear on fire:
> >
> >   $ upower -i /org/freedesktop/UPower/devices/battery_olpc_battery
> >   ...
> >       temperature:         236.9 degrees C
> >
> > Tested on OLPC XO-1 and OLPC XO-1.75 laptops.
> 
> It's interesting that the very author of that code is not included in
> so-o long Cc list :)
> Cc: David.
> 
> David, do you remember if and how you had tested temperature report of
> the battery on OLPC? I guess this kind of error would be appear immediately.

It depends on the way of testing. It's not so obvious when you just
do a `cat /sys/class/power_supply/.../temperature`, since you just
get the raw integer.

> OTOH it might be that power framework had changed requirements (which
> would be noticeable change).

As far as I know, power-supply has always used 1/10 °C. People tend
to get units wrong all the time though (i.e. mV instead of uV). I'm
not surprised, that this sneaked into the kernel.

> If the latter is true, this patch misses Fixes tag. Actually in any
> case it misses it.

Yes, this should probably have Fixes: fb972873a767 ("[BATTERY] One Laptop
Per Child power/battery driver").

-- Sebastian

> > [1] include/linux/power_supply.h
> > [2] Documentation/power/power_supply_class.txt
> >
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Lubomir Rintel <lkundrak@...sk>
> > ---
> >  drivers/power/supply/olpc_battery.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/power/supply/olpc_battery.c b/drivers/power/supply/olpc_battery.c
> > index 6da79ae14860..5a97e42a3547 100644
> > --- a/drivers/power/supply/olpc_battery.c
> > +++ b/drivers/power/supply/olpc_battery.c
> > @@ -428,14 +428,14 @@ static int olpc_bat_get_property(struct power_supply *psy,
> >                 if (ret)
> >                         return ret;
> >
> > -               val->intval = (s16)be16_to_cpu(ec_word) * 100 / 256;
> > +               val->intval = (s16)be16_to_cpu(ec_word) * 10 / 256;
> >                 break;
> >         case POWER_SUPPLY_PROP_TEMP_AMBIENT:
> >                 ret = olpc_ec_cmd(EC_AMB_TEMP, NULL, 0, (void *)&ec_word, 2);
> >                 if (ret)
> >                         return ret;
> >
> > -               val->intval = (int)be16_to_cpu(ec_word) * 100 / 256;
> > +               val->intval = (int)be16_to_cpu(ec_word) * 10 / 256;
> >                 break;
> >         case POWER_SUPPLY_PROP_CHARGE_COUNTER:
> >                 ret = olpc_ec_cmd(EC_BAT_ACR, NULL, 0, (void *)&ec_word, 2);
> > --
> > 2.19.0
> >
> 
> 
> -- 
> With Best Regards,
> Andy Shevchenko

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