linux-kernel - [PATCHv1] power: supply: document current direction

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Message-Id: <20200827140248.37749-1-sebastian.reichel@collabora.com>
Date:   Thu, 27 Aug 2020 16:02:48 +0200
From:   Sebastian Reichel <sebastian.reichel@...labora.com>
To:     Andreas Kemnade <andreas@...nade.info>,
        Sebastian Reichel <sre@...nel.org>
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com,
        Sebastian Reichel <sebastian.reichel@...labora.com>
Subject: [PATCHv1] 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@...labora.com>
---
 Documentation/ABI/testing/sysfs-class-power | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-class-power b/Documentation/ABI/testing/sysfs-class-power
index 651599fb18f8..dbccb2fcd7ce 100644
--- a/Documentation/ABI/testing/sysfs-class-power
+++ b/Documentation/ABI/testing/sysfs-class-power
@@ -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
-- 
2.28.0