ACPI: SBS: report relative state of charge as CAPACITY

acpi_sbs reads SBS command 0x0e (AbsoluteStateOfCharge) into
battery->state_of_charge, which is exported unmodified as
POWER_SUPPLY_PROP_CAPACITY.

Per the Smart Battery Data Specification 1.1, 0x0e is expressed as a
percentage of DesignCapacity and is explicitly permitted to exceed 100%.
Documentation/ABI/testing/sysfs-class-power specifies the capacity
attribute as "Valid values: 0 - 100 (percent)", so any pack whose
FullChargeCapacity exceeds its DesignCapacity - the normal state of a
new or recently replaced battery - makes the driver report out of range.

The correct source is 0x0d (RelativeStateOfCharge), a percentage of
FullChargeCapacity, which the specification bounds to 0..100.

This is the same defect that was fixed in the i2c SBS driver by commit
b1f092f6480e ("sbs-battery.c: Capacity attr = remaining relative
capacity"), whose reasoning applies verbatim here; drivers/acpi/sbs.c was
not updated at the time. drivers/power/supply/sbs-battery.c has used 0x0d
since, so the two SBS drivers currently disagree about what CAPACITY
means.

Observed on a MacBookPro11,1 with an SMP/bq20z451 pack
(FullChargeCapacity 6775 mAh, DesignCapacity 6400 mAh). Both registers
read back-to-back from the pack at a full charge:

  0x0d RelativeStateOfCharge = 100 %
  0x0e AbsoluteStateOfCharge = 106 %

/sys/class/power_supply/BAT0/capacity reported 106 while upower, which
computes charge_now/charge_full itself rather than trusting the driver,
reported 100.

battery->state_of_charge has no other consumer, so no other property
changes behaviour.

Signed-off-by: Itay Shem-tov <itayst@gmail.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://patch.msgid.link/20260903104244.25556-1-itayst@gmail.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

0 files changed, 0 insertions, 0 deletions