From: Itay Shem-tov <itayst@gmail.com>
To: rafael@kernel.org
Cc: lenb@kernel.org, linux-acpi@vger.kernel.org, sre@kernel.org,
linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
Itay Shem-tov <itayst@gmail.com>
Subject: [PATCH] ACPI: SBS: report relative state of charge as CAPACITY
Date: Thu, 3 Sep 2026 13:42:44 +0300 [thread overview]
Message-ID: <20260903104244.25556-1-itayst@gmail.com> (raw)
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>
---
drivers/acpi/sbs.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/acpi/sbs.c b/drivers/acpi/sbs.c
index 86b7c79..862cb94 100644
--- a/drivers/acpi/sbs.c
+++ b/drivers/acpi/sbs.c
@@ -318,7 +318,7 @@ static struct acpi_battery_reader state_readers[] = {
{0x0a, SMBUS_READ_WORD, offsetof(struct acpi_battery, rate_now)},
{0x0b, SMBUS_READ_WORD, offsetof(struct acpi_battery, rate_avg)},
{0x0f, SMBUS_READ_WORD, offsetof(struct acpi_battery, capacity_now)},
- {0x0e, SMBUS_READ_WORD, offsetof(struct acpi_battery, state_of_charge)},
+ {0x0d, SMBUS_READ_WORD, offsetof(struct acpi_battery, state_of_charge)},
{0x16, SMBUS_READ_WORD, offsetof(struct acpi_battery, state)},
};
--
2.51.0
reply other threads:[~2026-09-03 10:42 UTC|newest]
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