[PATCH v2 0/2] acpi: battery: Query BCT method and steamdeck

[PATCH v2 0/2] acpi: battery: Query BCT method and steamdeck

[Umang Jain]

Short series to query Battery charge time ("_BCT") from ACPI tables
(1/2).

Patch 2/2 handles the case where steamdeck devices can report "Charging"
even when low power PSU is connected which is discharging the device.

Changes in v2:
- comment improvements
- split off BCT method handling into separate patch

v1:
https://lore.kernel.org/all/20260918135628.2322188-1-uajain@igalia.com/

Umang Jain (2):
  acpi: battery: Query Battery charge time ("_BCT") method
  acpi: battery: Handle Valve steamdeck devices quirk

 drivers/acpi/battery.c | 45 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 44 insertions(+), 1 deletion(-)

-- 
2.55.0

[PATCH v2 1/2] acpi: battery: Query Battery charge time ("_BCT") method

[Umang Jain]

Add plumbing for querying the Battery Charge Time ("_BCT") method.
If present, set ACPI_BATTERY_BCT_PRESENT in battery flags to denote
that the method is supported in ACPI.

Signed-off-by: Umang Jain <uajain@igalia.com>
---
 drivers/acpi/battery.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/acpi/battery.c b/drivers/acpi/battery.c
index 670853ec3a4d..a1b7a821abaf 100644
--- a/drivers/acpi/battery.c
+++ b/drivers/acpi/battery.c
@@ -76,6 +76,7 @@ MODULE_DEVICE_TABLE(acpi, battery_device_ids);
 enum {
 	ACPI_BATTERY_ALARM_PRESENT,
 	ACPI_BATTERY_XINFO_PRESENT,
+	ACPI_BATTERY_BCT_PRESENT,
 	ACPI_BATTERY_QUIRK_PERCENTAGE_CAPACITY,
 	/* On Lenovo Thinkpad models from 2010 and 2011, the power unit
 	 * switches between mWh and mAh depending on whether the system
@@ -110,6 +111,7 @@ struct acpi_battery {
 
 	struct mutex property_lock; /* Protects properties below. */
 	unsigned long update_time;
+	unsigned long long charge_time;
 	int revision;
 	int rate_now;
 	int capacity_now;
@@ -613,6 +615,10 @@ static int acpi_battery_get_state(struct acpi_battery *battery)
 	int result = 0;
 	acpi_status status = 0;
 	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
+	union acpi_object arg0 = { ACPI_TYPE_INTEGER };
+	struct acpi_object_list args = { 1, &arg0 };
+
+	arg0.integer.value = 100;
 
 	lockdep_assert_held(&battery->property_lock);
 
@@ -638,6 +644,15 @@ static int acpi_battery_get_state(struct acpi_battery *battery)
 	battery->update_time = jiffies;
 	kfree(buffer.pointer);
 
+	if (test_bit(ACPI_BATTERY_BCT_PRESENT, &battery->flags)) {
+		status = acpi_evaluate_integer(battery->device->handle, "_BCT",
+					       &args, &battery->charge_time);
+	if (ACPI_FAILURE(status))
+		acpi_handle_info(battery->device->handle,
+				 "_BCT evaluation failed: %s",
+				 acpi_format_exception(status));
+	}
+
 	/* For buggy DSDTs that report negative 16-bit values for either
 	 * charging or discharging current and/or report 0 as 65536
 	 * due to bad math.
@@ -1083,6 +1098,8 @@ static int acpi_battery_update(struct acpi_battery *battery, bool resume)
 			if (result)
 				return result;
 			acpi_battery_init_alarm(battery);
+			if (acpi_has_method(battery->device->handle, "_BCT"))
+				set_bit(ACPI_BATTERY_BCT_PRESENT, &battery->flags);
 		}
 
 		result = acpi_battery_get_state(battery);
-- 
2.55.0

[PATCH v2 2/2] acpi: battery: Handle Valve steamdeck devices quirk

[Umang Jain]

Valve steamdeck devices can report battery status as
charging, even when low-powered power supply is connected
to the device. The battery status is reported as charging
through sysfs, even though in reality, it is discharging.

To handle this case, we introduce a battery quirk for steamdeck
devices ACPI_BATTERY_QUIRK_VALVE_STEAMDECK. Additionally, it has been
found that on such devices, Battery Charge Time ("_BCT") is reported
accurately, hence use that information for report charging vs
discharging status. Battery Charge Time("_BCT") with an eligible power
supply unit will have valid values whereas with a low-powered supply
unit, it shall report ACPI_BATTERY_VALUE_UNKNOWN. Use this as a
differentiator to determine, whether the battery of steamdeck devices
is really charging or not.

Signed-off-by: Umang Jain <uajain@igalia.com>
---
 drivers/acpi/battery.c | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/battery.c b/drivers/acpi/battery.c
index a1b7a821abaf..8defafd2b7c7 100644
--- a/drivers/acpi/battery.c
+++ b/drivers/acpi/battery.c
@@ -95,6 +95,14 @@ enum {
 	 * on a full charge, but showing degradation in full charge cap.
 	 */
 	ACPI_BATTERY_QUIRK_DEGRADED_FULL_CHARGE,
+	/*
+	 * Valve steamdeck devices can get discharged even when battery status
+	 * is charging. This happens typically when low power supply unit is
+	 * connected. To accurately determine this scenario, we shall read
+	 * battery charge time ("_BCT"). This is the key differentiator to
+	 * determine whether the steamdeck is actually charging or not.
+	 */
+	ACPI_BATTERY_QUIRK_VALVE_STEAMDECK,
 };
 
 struct acpi_battery {
@@ -236,7 +244,7 @@ static int acpi_battery_get_property(struct power_supply *psy,
 					: POWER_SUPPLY_STATUS_DISCHARGING;
 				return 0;
 			}
-		else if (battery->state & ACPI_BATTERY_STATE_CHARGING)
+		else if (battery->state & ACPI_BATTERY_STATE_CHARGING) {
 			/* Check the rate and capacity to validate the status. */
 			if (!acpi_battery_is_full(battery) ||
 			    (battery->rate_now != ACPI_BATTERY_VALUE_UNKNOWN &&
@@ -246,6 +254,12 @@ static int acpi_battery_get_property(struct power_supply *psy,
 				/* Full and zero rate. */
 				val->intval = POWER_SUPPLY_STATUS_NOT_CHARGING;
 			}
+
+			if (test_bit(ACPI_BATTERY_QUIRK_VALVE_STEAMDECK, &battery->flags) &&
+			    test_bit(ACPI_BATTERY_BCT_PRESENT, &battery->flags) &&
+			    battery->charge_time == ACPI_BATTERY_VALUE_UNKNOWN)
+				val->intval = POWER_SUPPLY_STATUS_DISCHARGING;
+		}
 		else if (battery->state & ACPI_BATTERY_STATE_CHARGE_LIMITING)
 			val->intval = POWER_SUPPLY_STATUS_NOT_CHARGING;
 		else if (acpi_battery_is_charged(battery))
@@ -1072,6 +1086,18 @@ static void acpi_battery_quirks(struct acpi_battery *battery)
 		set_bit(ACPI_BATTERY_QUIRK_DEGRADED_FULL_CHARGE, &battery->flags);
 		battery->capacity_now = battery->full_charge_capacity;
 	}
+
+	if (test_bit(ACPI_BATTERY_QUIRK_VALVE_STEAMDECK, &battery->flags))
+		return;
+
+	if (dmi_name_in_vendors("Valve")) {
+		const char *name;
+
+		name = dmi_get_system_info(DMI_PRODUCT_NAME);
+		if ((name && (!strncmp("Jupiter", name, 7))) ||
+		    (name && (!strncmp("Galileo", name, 7))))
+			set_bit(ACPI_BATTERY_QUIRK_VALVE_STEAMDECK, &battery->flags);
+	}
 }
 
 static int acpi_battery_update(struct acpi_battery *battery, bool resume)
-- 
2.55.0