linux-kernel - Re: [PATCH] power_supply: add CHARGE_COUNTER property and olpc

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Date:	Mon, 19 May 2008 01:46:56 +0400
From:	Anton Vorontsov <cbouatmailru@...il.com>
To:	Andres Salomon <dilinger@...ued.net>
Cc:	richard@...top.org, avorontsov@...mvista.com,
	Andrew Morton <akpm@...ux-foundation.org>, cbou@...l.ru,
	linux-kernel@...r.kernel.org, dwmw2@...radead.org
Subject: Re: [PATCH] power_supply: add CHARGE_COUNTER property and
	olpc_battery support for it

On Tue, May 13, 2008 at 12:23:30PM -0400, Andres Salomon wrote:
> On Tue, 13 May 2008 10:20:15 -0400
> "Richard A. Smith" <richard@...top.org> wrote:
> 
> > Andres Salomon wrote:
> > 
> > > +		ec_word = be16_to_cpu(ec_word);
> > > +		val->intval = ec_word * 4167 / 10;
> > 
> > Whats wrong with:
> > 
> >  > +		val->intval = ((int)ec_word) * 6250 / 15;
> > 
> > Which does not have overflow problems and keeps more precision.
> > 
> 
> You're right, of course.  Anton, can you please apply the following?

Sorry for the delay... Applied, thanks!

> Subject: [PATCH] power_supply: fix up CHARGE_COUNTER output to be more precise
> 
> As Richard Smith pointed out, ACR * 6250 / 15  provides for less precision
> loss than ACR * 4167 / 10, _and_ it doesn't overflow.  Switch to using
> that equation for CHARGE_COUNTER.
> 
> Signed-off-by: Andres Salomon <dilinger@...ian.org>
> ---
>  drivers/power/olpc_battery.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/power/olpc_battery.c b/drivers/power/olpc_battery.c
> index a928165..f5d712a 100644
> --- a/drivers/power/olpc_battery.c
> +++ b/drivers/power/olpc_battery.c
> @@ -19,7 +19,7 @@
>  
>  #define EC_BAT_VOLTAGE	0x10	/* uint16_t,	*9.76/32,    mV   */
>  #define EC_BAT_CURRENT	0x11	/* int16_t,	*15.625/120, mA   */
> -#define EC_BAT_ACR	0x12	/* int16_t,	*416.7,      µAh  */
> +#define EC_BAT_ACR	0x12	/* int16_t,	*6250/15,    µAh  */
>  #define EC_BAT_TEMP	0x13	/* uint16_t,	*100/256,   °C  */
>  #define EC_AMB_TEMP	0x14	/* uint16_t,	*100/256,   °C  */
>  #define EC_BAT_STATUS	0x15	/* uint8_t,	bitmask */
> @@ -295,7 +295,7 @@ static int olpc_bat_get_property(struct power_supply *psy,
>  			return ret;
>  
>  		ec_word = be16_to_cpu(ec_word);
> -		val->intval = ec_word * 4167 / 10;
> +		val->intval = ec_word * 6250 / 15;
>  		break;
>  	case POWER_SUPPLY_PROP_SERIAL_NUMBER:
>  		ret = olpc_ec_cmd(EC_BAT_SERIAL, NULL, 0, (void *)&ser_buf, 8);
> -- 
> 1.5.5.1

-- 
Anton Vorontsov
email: cbouatmailru@...il.com
irc://irc.freenode.net/bd2
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