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: Andres Salomon <dilinger@debian.org>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/Documentation/power/power_supply_class.txt b/Documentation/power/power_supply_class.txt
index a8686e5..c6cd495 100644
--- a/Documentation/power/power_supply_class.txt
+++ b/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.