ACPI: battery: negate current when discharging

The ACPI specification requires that battery rate is always positive,
but the kernel ABI for POWER_SUPPLY_PROP_CURRENT_NOW
(Documentation/ABI/testing/sysfs-class-power) specifies that it should
be negative when a battery is discharging. When reporting CURRENT_NOW,
massage the value to match the documented ABI.

This only changes the sign of `current_now` and not `power_now` because
documentation doesn't describe any particular meaning for `power_now` so
leaving `power_now` unchanged is less likely to confuse userspace
unnecessarily, whereas becoming consistent with the documented ABI is
worth potentially confusing clients that read `current_now`.

Signed-off-by: Peter Marheine <pmarheine@chromium.org>
Link: https://patch.msgid.link/20250508024146.1436129-1-pmarheine@chromium.org
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/acpi/battery.c b/drivers/acpi/battery.c
index 6905b56bf3e4580f2fb137e0a1101e13a47591d5..45593612a4db96260728ccad9009970c34c543d5 100644 (file)
--- a/drivers/acpi/battery.c
+++ b/drivers/acpi/battery.c
@@ -243,10 +243,23 @@ static int acpi_battery_get_property(struct power_supply *psy,
                break;
        case POWER_SUPPLY_PROP_CURRENT_NOW:
        case POWER_SUPPLY_PROP_POWER_NOW:
-               if (battery->rate_now == ACPI_BATTERY_VALUE_UNKNOWN)
+               if (battery->rate_now == ACPI_BATTERY_VALUE_UNKNOWN) {
                        ret = -ENODEV;
-               else
-                       val->intval = battery->rate_now * 1000;
+                       break;
+               }
+
+               val->intval = battery->rate_now * 1000;
+               /*
+                * When discharging, the current should be reported as a
+                * negative number as per the power supply class interface
+                * definition.
+                */
+               if (psp == POWER_SUPPLY_PROP_CURRENT_NOW &&
+                   (battery->state & ACPI_BATTERY_STATE_DISCHARGING) &&
+                   acpi_battery_handle_discharging(battery)
+                               == POWER_SUPPLY_STATUS_DISCHARGING)
+                       val->intval = -val->intval;
+
                break;
        case POWER_SUPPLY_PROP_CHARGE_FULL_DESIGN:
        case POWER_SUPPLY_PROP_ENERGY_FULL_DESIGN: