power_supply: add CHARGE_COUNTER property and olpc_battery support for it

This adds PROP_CHARGE_COUNTER to the power supply class (documenting it
as well).  The OLPC battery driver uses this for spitting out its ACR
values (in uAh).  We have some rounding errors (the data sheet claims
416.7, the math actually works out to 416.666667, so we're forced to
choose between overflows or precision loss.  I chose precision loss,
and stuck w/ data sheet values), but I don't think anyone will care
that much.
Signed-off-by: NAndres Salomon <dilinger@debian.org>
Signed-off-by: NAnton Vorontsov <cbouatmailru@gmail.com>

Documentation/power/power_supply_class.txt

@@ -101,6 +101,10 @@ of charge when battery became full/empty". It also could mean "value of
 charge when battery considered full/empty at given conditions (temperature,
 age)". I.e. these attributes represents real thresholds, not design values.
 
+CHARGE_COUNTER - the current charge counter (in µAh).  This could easily
+be negative; there is no empty or full value.  It is only useful for
+relative, time-based measurements.
+
 ENERGY_FULL, ENERGY_EMPTY - same as above but for energy.
 
 CAPACITY - capacity in percents.

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
+#define EC_BAT_ACR	0x12	/* int16_t,	*416.7,      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 */
@@ -289,6 +289,14 @@ static int olpc_bat_get_property(struct power_supply *psy,
 		ec_word = be16_to_cpu(ec_word);
 		val->intval = ec_word * 100 / 256;
 		break;
+	case POWER_SUPPLY_PROP_CHARGE_COUNTER:
+		ret = olpc_ec_cmd(EC_BAT_ACR, NULL, 0, (void *)&ec_word, 2);
+		if (ret)
+			return ret;
+
+		ec_word = be16_to_cpu(ec_word);
+		val->intval = ec_word * 4167 / 10;
+		break;
 	case POWER_SUPPLY_PROP_SERIAL_NUMBER:
 		ret = olpc_ec_cmd(EC_BAT_SERIAL, NULL, 0, (void *)&ser_buf, 8);
 		if (ret)
@@ -317,6 +325,7 @@ static enum power_supply_property olpc_bat_props[] = {
 	POWER_SUPPLY_PROP_TEMP_AMBIENT,
 	POWER_SUPPLY_PROP_MANUFACTURER,
 	POWER_SUPPLY_PROP_SERIAL_NUMBER,
+	POWER_SUPPLY_PROP_CHARGE_COUNTER,
 };
 
 /* EEPROM reading goes completely around the power_supply API, sadly */

drivers/power/power_supply_sysfs.c

@@ -99,6 +99,7 @@ static struct device_attribute power_supply_attrs[] = {
 	POWER_SUPPLY_ATTR(charge_empty),
 	POWER_SUPPLY_ATTR(charge_now),
 	POWER_SUPPLY_ATTR(charge_avg),
+	POWER_SUPPLY_ATTR(charge_counter),
 	POWER_SUPPLY_ATTR(energy_full_design),
 	POWER_SUPPLY_ATTR(energy_empty_design),
 	POWER_SUPPLY_ATTR(energy_full),

include/linux/power_supply.h

@@ -78,6 +78,7 @@ enum power_supply_property {
 	POWER_SUPPLY_PROP_CHARGE_EMPTY,
 	POWER_SUPPLY_PROP_CHARGE_NOW,
 	POWER_SUPPLY_PROP_CHARGE_AVG,
+	POWER_SUPPLY_PROP_CHARGE_COUNTER,
 	POWER_SUPPLY_PROP_ENERGY_FULL_DESIGN,
 	POWER_SUPPLY_PROP_ENERGY_EMPTY_DESIGN,
 	POWER_SUPPLY_PROP_ENERGY_FULL,