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SubjectRe: [PATCH] power_supply: add CHARGE_COUNTER property and olpc_battery support for it
On Tue, 13 May 2008 10:20:15 -0400
"Richard A. Smith" <richard@laptop.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?



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@debian.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
--
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