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power: supply: document current direction 

Currently the sign for CURRENT_NOW and CURRENT_AVG is a bit
of a mess. There are basically 3 different ways battery fuel
gauges report the current:

1. uses negative values for discharging and positive values
   for charging
2. uses positive values for discharging and negative values
   for discharging (opposit of 1)
3. only uses positive values

As a result userspace currently cannot use the sign at all in
a generic way. Let's solve the issue by documenting a canonical
way for reporting the data and ensure new drivers follow this
way. Then existing drivers can be fixed on a case-by-case basis.

The 'negative value = battery discharging' has been choosen,
since there are only very few drivers doing it the other way
around.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
This commit is contained in:
Sebastian Reichel 2020-08-27 16:02:48 +02:00
parent 41a7431dba
commit 05f94eb989
1 changed files with 4 additions and 2 deletions
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Documentation/ABI/testing/sysfs-class-power
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@ -108,7 +108,8 @@ Description:
which they average readings to smooth out the reported value.
Access: Read
Valid values: Represented in microamps
Valid values: Represented in microamps. Negative values are used
for discharging batteries, positive values for charging batteries.
What: /sys/class/power_supply/<supply_name>/current_max
Date: October 2010
@ -127,7 +128,8 @@ Description:
This value is not averaged/smoothed.
Access: Read
Valid values: Represented in microamps
Valid values: Represented in microamps. Negative values are used
for discharging batteries, positive values for charging batteries.
What: /sys/class/power_supply/<supply_name>/charge_control_limit
Date: Oct 2012