power: supply: Add battery driver for Surface Aggregator Module

On newer Microsoft Surface models (specifically 7th-generation, i.e.
Surface Pro 7, Surface Book 3, Surface Laptop 3, and Surface Laptop Go),
battery and AC status/information is no longer handled via standard ACPI
devices, but instead directly via the Surface System Aggregator Module
(SSAM), i.e. the embedded controller on those devices.

While on previous generation models, battery status is also handled via
SSAM, an ACPI shim was present to translate the standard ACPI battery
interface to SSAM requests. The SSAM interface itself, which is modeled
closely after the ACPI interface, has not changed.

This commit introduces a new SSAM client device driver to support
battery status/information via the aforementioned interface on said
Surface models. It is in parts based on the standard ACPI battery
driver.
Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Documentation/ABI/testing/sysfs-class-power-surface

+What:		/sys/class/power_supply/<supply_name>/alarm
+Date:		April 2021
+KernelVersion:	5.13
+Contact:	Maximilian Luz <luzmaximilian@gmail.com>
+Description:
+		Battery trip point. When the remaining battery capacity crosses this
+		value in either direction, the system will be notified and if
+		necessary woken.
+
+		Set to zero to clear/disable.
+
+		Access: Read, Write
+
+		Valid values: In micro-Wh or micro-Ah, depending on the power unit
+		of the battery

MAINTAINERS

@@ -11861,6 +11861,13 @@ F:	drivers/scsi/smartpqi/smartpqi*.[ch]
 F:	include/linux/cciss*.h
 F:	include/uapi/linux/cciss*.h
 
+MICROSOFT SURFACE BATTERY AND AC DRIVERS
+M:	Maximilian Luz <luzmaximilian@gmail.com>
+L:	linux-pm@vger.kernel.org
+L:	platform-driver-x86@vger.kernel.org
+S:	Maintained
+F:	drivers/power/supply/surface_battery.c
+
 MICROSOFT SURFACE GPE LID SUPPORT DRIVER
 M:	Maximilian Luz <luzmaximilian@gmail.com>
 L:	platform-driver-x86@vger.kernel.org

drivers/power/supply/Kconfig

@@ -801,4 +801,20 @@ config BATTERY_ACER_A500
 	help
 	  Say Y to include support for Acer Iconia Tab A500 battery fuel gauge.
 
+config BATTERY_SURFACE
+	tristate "Battery driver for 7th-generation Microsoft Surface devices"
+	depends on SURFACE_AGGREGATOR_REGISTRY
+	help
+	  Driver for battery devices connected via/managed by the Surface System
+	  Aggregator Module (SSAM).
+
+	  This driver provides battery-information and -status support for
+	  Surface devices where said data is not exposed via the standard ACPI
+	  devices. On those models (7th-generation), battery-information is
+	  instead handled directly via SSAM client devices and this driver.
+
+	  Say M or Y here to include battery status support for 7th-generation
+	  Microsoft Surface devices, i.e. Surface Pro 7, Surface Laptop 3,
+	  Surface Book 3, and Surface Laptop Go.
+
 endif # POWER_SUPPLY

drivers/power/supply/Makefile

@@ -101,3 +101,4 @@ obj-$(CONFIG_CHARGER_BD99954)	+= bd99954-charger.o
 obj-$(CONFIG_CHARGER_WILCO)	+= wilco-charger.o
 obj-$(CONFIG_RN5T618_POWER)	+= rn5t618_power.o
 obj-$(CONFIG_BATTERY_ACER_A500)	+= acer_a500_battery.o
+obj-$(CONFIG_BATTERY_SURFACE)	+= surface_battery.o

drivers/power/supply/surface_battery.c

+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Battery driver for 7th-generation Microsoft Surface devices via Surface
+ * System Aggregator Module (SSAM).
+ *
+ * Copyright (C) 2019-2021 Maximilian Luz <luzmaximilian@gmail.com>
+ */
+
+#include <asm/unaligned.h>
+#include <linux/jiffies.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/power_supply.h>
+#include <linux/sysfs.h>
+#include <linux/types.h>
+#include <linux/workqueue.h>
+
+#include <linux/surface_aggregator/device.h>
+
+
+/* -- SAM interface. -------------------------------------------------------- */
+
+enum sam_event_cid_bat {
+	SAM_EVENT_CID_BAT_BIX         = 0x15,
+	SAM_EVENT_CID_BAT_BST         = 0x16,
+	SAM_EVENT_CID_BAT_ADP         = 0x17,
+	SAM_EVENT_CID_BAT_PROT        = 0x18,
+	SAM_EVENT_CID_BAT_DPTF        = 0x53,
+};
+
+enum sam_battery_sta {
+	SAM_BATTERY_STA_OK            = 0x0f,
+	SAM_BATTERY_STA_PRESENT	      = 0x10,
+};
+
+enum sam_battery_state {
+	SAM_BATTERY_STATE_DISCHARGING = BIT(0),
+	SAM_BATTERY_STATE_CHARGING    = BIT(1),
+	SAM_BATTERY_STATE_CRITICAL    = BIT(2),
+};
+
+enum sam_battery_power_unit {
+	SAM_BATTERY_POWER_UNIT_mW     = 0,
+	SAM_BATTERY_POWER_UNIT_mA     = 1,
+};
+
+/* Equivalent to data returned in ACPI _BIX method, revision 0. */
+struct spwr_bix {
+	u8  revision;
+	__le32 power_unit;
+	__le32 design_cap;
+	__le32 last_full_charge_cap;
+	__le32 technology;
+	__le32 design_voltage;
+	__le32 design_cap_warn;
+	__le32 design_cap_low;
+	__le32 cycle_count;
+	__le32 measurement_accuracy;
+	__le32 max_sampling_time;
+	__le32 min_sampling_time;
+	__le32 max_avg_interval;
+	__le32 min_avg_interval;
+	__le32 bat_cap_granularity_1;
+	__le32 bat_cap_granularity_2;
+	__u8 model[21];
+	__u8 serial[11];
+	__u8 type[5];
+	__u8 oem_info[21];
+} __packed;
+
+static_assert(sizeof(struct spwr_bix) == 119);
+
+/* Equivalent to data returned in ACPI _BST method. */
+struct spwr_bst {
+	__le32 state;
+	__le32 present_rate;
+	__le32 remaining_cap;
+	__le32 present_voltage;
+} __packed;
+
+static_assert(sizeof(struct spwr_bst) == 16);
+
+#define SPWR_BIX_REVISION		0
+#define SPWR_BATTERY_VALUE_UNKNOWN	0xffffffff
+
+/* Get battery status (_STA) */
+SSAM_DEFINE_SYNC_REQUEST_CL_R(ssam_bat_get_sta, __le32, {
+	.target_category = SSAM_SSH_TC_BAT,
+	.command_id      = 0x01,
+});
+
+/* Get battery static information (_BIX). */
+SSAM_DEFINE_SYNC_REQUEST_CL_R(ssam_bat_get_bix, struct spwr_bix, {
+	.target_category = SSAM_SSH_TC_BAT,
+	.command_id      = 0x02,
+});
+
+/* Get battery dynamic information (_BST). */
+SSAM_DEFINE_SYNC_REQUEST_CL_R(ssam_bat_get_bst, struct spwr_bst, {
+	.target_category = SSAM_SSH_TC_BAT,
+	.command_id      = 0x03,
+});
+
+/* Set battery trip point (_BTP). */
+SSAM_DEFINE_SYNC_REQUEST_CL_W(ssam_bat_set_btp, __le32, {
+	.target_category = SSAM_SSH_TC_BAT,
+	.command_id      = 0x04,
+});
+
+
+/* -- Device structures. ---------------------------------------------------- */
+
+struct spwr_psy_properties {
+	const char *name;
+	struct ssam_event_registry registry;
+};
+
+struct spwr_battery_device {
+	struct ssam_device *sdev;
+
+	char name[32];
+	struct power_supply *psy;
+	struct power_supply_desc psy_desc;
+
+	struct delayed_work update_work;
+
+	struct ssam_event_notifier notif;
+
+	struct mutex lock;  /* Guards access to state data below. */
+	unsigned long timestamp;
+
+	__le32 sta;
+	struct spwr_bix bix;
+	struct spwr_bst bst;
+	u32 alarm;
+};
+
+
+/* -- Module parameters. ---------------------------------------------------- */
+
+static unsigned int cache_time = 1000;
+module_param(cache_time, uint, 0644);
+MODULE_PARM_DESC(cache_time, "battery state caching time in milliseconds [default: 1000]");
+
+
+/* -- State management. ----------------------------------------------------- */
+
+/*
+ * Delay for battery update quirk. See spwr_external_power_changed() below
+ * for more details.
+ */
+#define SPWR_AC_BAT_UPDATE_DELAY	msecs_to_jiffies(5000)
+
+static bool spwr_battery_present(struct spwr_battery_device *bat)
+{
+	lockdep_assert_held(&bat->lock);
+
+	return le32_to_cpu(bat->sta) & SAM_BATTERY_STA_PRESENT;
+}
+
+static int spwr_battery_load_sta(struct spwr_battery_device *bat)
+{
+	lockdep_assert_held(&bat->lock);
+
+	return ssam_retry(ssam_bat_get_sta, bat->sdev, &bat->sta);
+}
+
+static int spwr_battery_load_bix(struct spwr_battery_device *bat)
+{
+	int status;
+
+	lockdep_assert_held(&bat->lock);
+
+	if (!spwr_battery_present(bat))
+		return 0;
+
+	status = ssam_retry(ssam_bat_get_bix, bat->sdev, &bat->bix);
+
+	/* Enforce NULL terminated strings in case anything goes wrong... */
+	bat->bix.model[ARRAY_SIZE(bat->bix.model) - 1] = 0;
+	bat->bix.serial[ARRAY_SIZE(bat->bix.serial) - 1] = 0;
+	bat->bix.type[ARRAY_SIZE(bat->bix.type) - 1] = 0;
+	bat->bix.oem_info[ARRAY_SIZE(bat->bix.oem_info) - 1] = 0;
+
+	return status;
+}
+
+static int spwr_battery_load_bst(struct spwr_battery_device *bat)
+{
+	lockdep_assert_held(&bat->lock);
+
+	if (!spwr_battery_present(bat))
+		return 0;
+
+	return ssam_retry(ssam_bat_get_bst, bat->sdev, &bat->bst);
+}
+
+static int spwr_battery_set_alarm_unlocked(struct spwr_battery_device *bat, u32 value)
+{
+	__le32 value_le = cpu_to_le32(value);
+
+	lockdep_assert_held(&bat->lock);
+
+	bat->alarm = value;
+	return ssam_retry(ssam_bat_set_btp, bat->sdev, &value_le);
+}
+
+static int spwr_battery_update_bst_unlocked(struct spwr_battery_device *bat, bool cached)
+{
+	unsigned long cache_deadline = bat->timestamp + msecs_to_jiffies(cache_time);
+	int status;
+
+	lockdep_assert_held(&bat->lock);
+
+	if (cached && bat->timestamp && time_is_after_jiffies(cache_deadline))
+		return 0;
+
+	status = spwr_battery_load_sta(bat);
+	if (status)
+		return status;
+
+	status = spwr_battery_load_bst(bat);
+	if (status)
+		return status;
+
+	bat->timestamp = jiffies;
+	return 0;
+}
+
+static int spwr_battery_update_bst(struct spwr_battery_device *bat, bool cached)
+{
+	int status;
+
+	mutex_lock(&bat->lock);
+	status = spwr_battery_update_bst_unlocked(bat, cached);
+	mutex_unlock(&bat->lock);
+
+	return status;
+}
+
+static int spwr_battery_update_bix_unlocked(struct spwr_battery_device *bat)
+{
+	int status;
+
+	lockdep_assert_held(&bat->lock);
+
+	status = spwr_battery_load_sta(bat);
+	if (status)
+		return status;
+
+	status = spwr_battery_load_bix(bat);
+	if (status)
+		return status;
+
+	status = spwr_battery_load_bst(bat);
+	if (status)
+		return status;
+
+	if (bat->bix.revision != SPWR_BIX_REVISION)
+		dev_warn(&bat->sdev->dev, "unsupported battery revision: %u\n", bat->bix.revision);
+
+	bat->timestamp = jiffies;
+	return 0;
+}
+
+static u32 sprw_battery_get_full_cap_safe(struct spwr_battery_device *bat)
+{
+	u32 full_cap = get_unaligned_le32(&bat->bix.last_full_charge_cap);
+
+	lockdep_assert_held(&bat->lock);
+
+	if (full_cap == 0 || full_cap == SPWR_BATTERY_VALUE_UNKNOWN)
+		full_cap = get_unaligned_le32(&bat->bix.design_cap);
+
+	return full_cap;
+}
+
+static bool spwr_battery_is_full(struct spwr_battery_device *bat)
+{
+	u32 state = get_unaligned_le32(&bat->bst.state);
+	u32 full_cap = sprw_battery_get_full_cap_safe(bat);
+	u32 remaining_cap = get_unaligned_le32(&bat->bst.remaining_cap);
+
+	lockdep_assert_held(&bat->lock);
+
+	return full_cap != SPWR_BATTERY_VALUE_UNKNOWN && full_cap != 0 &&
+		remaining_cap != SPWR_BATTERY_VALUE_UNKNOWN &&
+		remaining_cap >= full_cap &&
+		state == 0;
+}
+
+static int spwr_battery_recheck_full(struct spwr_battery_device *bat)
+{
+	bool present;
+	u32 unit;
+	int status;
+
+	mutex_lock(&bat->lock);
+	unit = get_unaligned_le32(&bat->bix.power_unit);
+	present = spwr_battery_present(bat);
+
+	status = spwr_battery_update_bix_unlocked(bat);
+	if (status)
+		goto out;
+
+	/* If battery has been attached, (re-)initialize alarm. */
+	if (!present && spwr_battery_present(bat)) {
+		u32 cap_warn = get_unaligned_le32(&bat->bix.design_cap_warn);
+
+		status = spwr_battery_set_alarm_unlocked(bat, cap_warn);
+		if (status)
+			goto out;
+	}
+
+	/*
+	 * Warn if the unit has changed. This is something we genuinely don't
+	 * expect to happen, so make this a big warning. If it does, we'll
+	 * need to add support for it.
+	 */
+	WARN_ON(unit != get_unaligned_le32(&bat->bix.power_unit));
+
+out:
+	mutex_unlock(&bat->lock);
+
+	if (!status)
+		power_supply_changed(bat->psy);
+
+	return status;
+}
+
+static int spwr_battery_recheck_status(struct spwr_battery_device *bat)
+{
+	int status;
+
+	status = spwr_battery_update_bst(bat, false);
+	if (!status)
+		power_supply_changed(bat->psy);
+
+	return status;
+}
+
+static u32 spwr_notify_bat(struct ssam_event_notifier *nf, const struct ssam_event *event)
+{
+	struct spwr_battery_device *bat = container_of(nf, struct spwr_battery_device, notif);
+	int status;
+
+	dev_dbg(&bat->sdev->dev, "power event (cid = %#04x, iid = %#04x, tid = %#04x)\n",
+		event->command_id, event->instance_id, event->target_id);
+
+	switch (event->command_id) {
+	case SAM_EVENT_CID_BAT_BIX:
+		status = spwr_battery_recheck_full(bat);
+		break;
+
+	case SAM_EVENT_CID_BAT_BST:
+		status = spwr_battery_recheck_status(bat);
+		break;
+
+	case SAM_EVENT_CID_BAT_PROT:
+		/*
+		 * TODO: Implement support for battery protection status change
+		 *       event.
+		 */
+		status = 0;
+		break;
+
+	case SAM_EVENT_CID_BAT_DPTF:
+		/*
+		 * TODO: Implement support for DPTF event.
+		 */
+		status = 0;
+		break;
+
+	default:
+		return 0;
+	}
+
+	return ssam_notifier_from_errno(status) | SSAM_NOTIF_HANDLED;
+}
+
+static void spwr_battery_update_bst_workfn(struct work_struct *work)
+{
+	struct delayed_work *dwork = to_delayed_work(work);
+	struct spwr_battery_device *bat;
+	int status;
+
+	bat = container_of(dwork, struct spwr_battery_device, update_work);
+
+	status = spwr_battery_update_bst(bat, false);
+	if (status) {
+		dev_err(&bat->sdev->dev, "failed to update battery state: %d\n", status);
+		return;
+	}
+
+	power_supply_changed(bat->psy);
+}
+
+static void spwr_external_power_changed(struct power_supply *psy)
+{
+	struct spwr_battery_device *bat = power_supply_get_drvdata(psy);
+
+	/*
+	 * Handle battery update quirk: When the battery is fully charged (or
+	 * charged up to the limit imposed by the UEFI battery limit) and the
+	 * adapter is plugged in or removed, the EC does not send a separate
+	 * event for the state (charging/discharging) change. Furthermore it
+	 * may take some time until the state is updated on the battery.
+	 * Schedule an update to solve this.
+	 */
+
+	schedule_delayed_work(&bat->update_work, SPWR_AC_BAT_UPDATE_DELAY);
+}
+
+
+/* -- Properties. ----------------------------------------------------------- */
+
+static const enum power_supply_property spwr_battery_props_chg[] = {
+	POWER_SUPPLY_PROP_STATUS,
+	POWER_SUPPLY_PROP_PRESENT,
+	POWER_SUPPLY_PROP_TECHNOLOGY,
+	POWER_SUPPLY_PROP_CYCLE_COUNT,
+	POWER_SUPPLY_PROP_VOLTAGE_MIN_DESIGN,
+	POWER_SUPPLY_PROP_VOLTAGE_NOW,
+	POWER_SUPPLY_PROP_CURRENT_NOW,
+	POWER_SUPPLY_PROP_CHARGE_FULL_DESIGN,
+	POWER_SUPPLY_PROP_CHARGE_FULL,
+	POWER_SUPPLY_PROP_CHARGE_NOW,
+	POWER_SUPPLY_PROP_CAPACITY,
+	POWER_SUPPLY_PROP_CAPACITY_LEVEL,
+	POWER_SUPPLY_PROP_MODEL_NAME,
+	POWER_SUPPLY_PROP_MANUFACTURER,
+	POWER_SUPPLY_PROP_SERIAL_NUMBER,
+};
+
+static const enum power_supply_property spwr_battery_props_eng[] = {
+	POWER_SUPPLY_PROP_STATUS,
+	POWER_SUPPLY_PROP_PRESENT,
+	POWER_SUPPLY_PROP_TECHNOLOGY,
+	POWER_SUPPLY_PROP_CYCLE_COUNT,
+	POWER_SUPPLY_PROP_VOLTAGE_MIN_DESIGN,
+	POWER_SUPPLY_PROP_VOLTAGE_NOW,
+	POWER_SUPPLY_PROP_POWER_NOW,
+	POWER_SUPPLY_PROP_ENERGY_FULL_DESIGN,
+	POWER_SUPPLY_PROP_ENERGY_FULL,
+	POWER_SUPPLY_PROP_ENERGY_NOW,
+	POWER_SUPPLY_PROP_CAPACITY,
+	POWER_SUPPLY_PROP_CAPACITY_LEVEL,
+	POWER_SUPPLY_PROP_MODEL_NAME,
+	POWER_SUPPLY_PROP_MANUFACTURER,
+	POWER_SUPPLY_PROP_SERIAL_NUMBER,
+};
+
+static int spwr_battery_prop_status(struct spwr_battery_device *bat)
+{
+	u32 state = get_unaligned_le32(&bat->bst.state);
+	u32 present_rate = get_unaligned_le32(&bat->bst.present_rate);
+
+	lockdep_assert_held(&bat->lock);
+
+	if (state & SAM_BATTERY_STATE_DISCHARGING)
+		return POWER_SUPPLY_STATUS_DISCHARGING;
+
+	if (state & SAM_BATTERY_STATE_CHARGING)
+		return POWER_SUPPLY_STATUS_CHARGING;
+
+	if (spwr_battery_is_full(bat))
+		return POWER_SUPPLY_STATUS_FULL;
+
+	if (present_rate == 0)
+		return POWER_SUPPLY_STATUS_NOT_CHARGING;
+
+	return POWER_SUPPLY_STATUS_UNKNOWN;
+}
+
+static int spwr_battery_prop_technology(struct spwr_battery_device *bat)
+{
+	lockdep_assert_held(&bat->lock);
+
+	if (!strcasecmp("NiCd", bat->bix.type))
+		return POWER_SUPPLY_TECHNOLOGY_NiCd;
+
+	if (!strcasecmp("NiMH", bat->bix.type))
+		return POWER_SUPPLY_TECHNOLOGY_NiMH;
+
+	if (!strcasecmp("LION", bat->bix.type))
+		return POWER_SUPPLY_TECHNOLOGY_LION;
+
+	if (!strncasecmp("LI-ION", bat->bix.type, 6))
+		return POWER_SUPPLY_TECHNOLOGY_LION;
+
+	if (!strcasecmp("LiP", bat->bix.type))
+		return POWER_SUPPLY_TECHNOLOGY_LIPO;
+
+	return POWER_SUPPLY_TECHNOLOGY_UNKNOWN;
+}
+
+static int spwr_battery_prop_capacity(struct spwr_battery_device *bat)
+{
+	u32 full_cap = sprw_battery_get_full_cap_safe(bat);
+	u32 remaining_cap = get_unaligned_le32(&bat->bst.remaining_cap);
+
+	lockdep_assert_held(&bat->lock);
+
+	if (full_cap == 0 || full_cap == SPWR_BATTERY_VALUE_UNKNOWN)
+		return -ENODATA;
+
+	if (remaining_cap == SPWR_BATTERY_VALUE_UNKNOWN)
+		return -ENODATA;
+
+	return remaining_cap * 100 / full_cap;
+}
+
+static int spwr_battery_prop_capacity_level(struct spwr_battery_device *bat)
+{
+	u32 state = get_unaligned_le32(&bat->bst.state);
+	u32 remaining_cap = get_unaligned_le32(&bat->bst.remaining_cap);
+
+	lockdep_assert_held(&bat->lock);
+
+	if (state & SAM_BATTERY_STATE_CRITICAL)
+		return POWER_SUPPLY_CAPACITY_LEVEL_CRITICAL;
+
+	if (spwr_battery_is_full(bat))
+		return POWER_SUPPLY_CAPACITY_LEVEL_FULL;
+
+	if (remaining_cap <= bat->alarm)
+		return POWER_SUPPLY_CAPACITY_LEVEL_LOW;
+
+	return POWER_SUPPLY_CAPACITY_LEVEL_NORMAL;
+}
+
+static int spwr_battery_get_property(struct power_supply *psy, enum power_supply_property psp,
+				     union power_supply_propval *val)
+{
+	struct spwr_battery_device *bat = power_supply_get_drvdata(psy);
+	u32 value;
+	int status;
+
+	mutex_lock(&bat->lock);
+
+	status = spwr_battery_update_bst_unlocked(bat, true);
+	if (status)
+		goto out;
+
+	/* Abort if battery is not present. */
+	if (!spwr_battery_present(bat) && psp != POWER_SUPPLY_PROP_PRESENT) {
+		status = -ENODEV;
+		goto out;
+	}
+
+	switch (psp) {
+	case POWER_SUPPLY_PROP_STATUS:
+		val->intval = spwr_battery_prop_status(bat);
+		break;
+
+	case POWER_SUPPLY_PROP_PRESENT:
+		val->intval = spwr_battery_present(bat);
+		break;
+
+	case POWER_SUPPLY_PROP_TECHNOLOGY:
+		val->intval = spwr_battery_prop_technology(bat);
+		break;
+
+	case POWER_SUPPLY_PROP_CYCLE_COUNT:
+		value = get_unaligned_le32(&bat->bix.cycle_count);
+		if (value != SPWR_BATTERY_VALUE_UNKNOWN)
+			val->intval = value;
+		else
+			status = -ENODATA;
+		break;
+
+	case POWER_SUPPLY_PROP_VOLTAGE_MIN_DESIGN:
+		value = get_unaligned_le32(&bat->bix.design_voltage);
+		if (value != SPWR_BATTERY_VALUE_UNKNOWN)
+			val->intval = value * 1000;
+		else
+			status = -ENODATA;
+		break;
+
+	case POWER_SUPPLY_PROP_VOLTAGE_NOW:
+		value = get_unaligned_le32(&bat->bst.present_voltage);
+		if (value != SPWR_BATTERY_VALUE_UNKNOWN)
+			val->intval = value * 1000;
+		else
+			status = -ENODATA;
+		break;
+
+	case POWER_SUPPLY_PROP_CURRENT_NOW:
+	case POWER_SUPPLY_PROP_POWER_NOW:
+		value = get_unaligned_le32(&bat->bst.present_rate);
+		if (value != SPWR_BATTERY_VALUE_UNKNOWN)
+			val->intval = value * 1000;
+		else
+			status = -ENODATA;
+		break;
+
+	case POWER_SUPPLY_PROP_CHARGE_FULL_DESIGN:
+	case POWER_SUPPLY_PROP_ENERGY_FULL_DESIGN:
+		value = get_unaligned_le32(&bat->bix.design_cap);
+		if (value != SPWR_BATTERY_VALUE_UNKNOWN)
+			val->intval = value * 1000;
+		else
+			status = -ENODATA;
+		break;
+
+	case POWER_SUPPLY_PROP_CHARGE_FULL:
+	case POWER_SUPPLY_PROP_ENERGY_FULL:
+		value = get_unaligned_le32(&bat->bix.last_full_charge_cap);
+		if (value != SPWR_BATTERY_VALUE_UNKNOWN)
+			val->intval = value * 1000;
+		else
+			status = -ENODATA;
+		break;
+
+	case POWER_SUPPLY_PROP_CHARGE_NOW:
+	case POWER_SUPPLY_PROP_ENERGY_NOW:
+		value = get_unaligned_le32(&bat->bst.remaining_cap);
+		if (value != SPWR_BATTERY_VALUE_UNKNOWN)
+			val->intval = value * 1000;
+		else
+			status = -ENODATA;
+		break;
+
+	case POWER_SUPPLY_PROP_CAPACITY:
+		val->intval = spwr_battery_prop_capacity(bat);
+		break;
+
+	case POWER_SUPPLY_PROP_CAPACITY_LEVEL:
+		val->intval = spwr_battery_prop_capacity_level(bat);
+		break;
+
+	case POWER_SUPPLY_PROP_MODEL_NAME:
+		val->strval = bat->bix.model;
+		break;
+
+	case POWER_SUPPLY_PROP_MANUFACTURER:
+		val->strval = bat->bix.oem_info;
+		break;
+
+	case POWER_SUPPLY_PROP_SERIAL_NUMBER:
+		val->strval = bat->bix.serial;
+		break;
+
+	default:
+		status = -EINVAL;
+		break;
+	}
+
+out:
+	mutex_unlock(&bat->lock);
+	return status;
+}
+
+
+/* -- Alarm attribute. ------------------------------------------------------ */
+
+static ssize_t alarm_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct power_supply *psy = dev_get_drvdata(dev);
+	struct spwr_battery_device *bat = power_supply_get_drvdata(psy);
+	int status;
+
+	mutex_lock(&bat->lock);
+	status = sysfs_emit(buf, "%d\n", bat->alarm * 1000);
+	mutex_unlock(&bat->lock);
+
+	return status;
+}
+
+static ssize_t alarm_store(struct device *dev, struct device_attribute *attr, const char *buf,
+			   size_t count)
+{
+	struct power_supply *psy = dev_get_drvdata(dev);
+	struct spwr_battery_device *bat = power_supply_get_drvdata(psy);
+	unsigned long value;
+	int status;
+
+	status = kstrtoul(buf, 0, &value);
+	if (status)
+		return status;
+
+	mutex_lock(&bat->lock);
+
+	if (!spwr_battery_present(bat)) {
+		mutex_unlock(&bat->lock);
+		return -ENODEV;
+	}
+
+	status = spwr_battery_set_alarm_unlocked(bat, value / 1000);
+	if (status) {
+		mutex_unlock(&bat->lock);
+		return status;
+	}
+
+	mutex_unlock(&bat->lock);
+	return count;
+}
+
+DEVICE_ATTR_RW(alarm);
+
+static struct attribute *spwr_battery_attrs[] = {
+	&dev_attr_alarm.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(spwr_battery);
+
+
+/* -- Device setup. --------------------------------------------------------- */
+
+static void spwr_battery_init(struct spwr_battery_device *bat, struct ssam_device *sdev,
+			      struct ssam_event_registry registry, const char *name)
+{
+	mutex_init(&bat->lock);
+	strncpy(bat->name, name, ARRAY_SIZE(bat->name) - 1);
+
+	bat->sdev = sdev;
+
+	bat->notif.base.priority = 1;
+	bat->notif.base.fn = spwr_notify_bat;
+	bat->notif.event.reg = registry;
+	bat->notif.event.id.target_category = sdev->uid.category;
+	bat->notif.event.id.instance = 0;
+	bat->notif.event.mask = SSAM_EVENT_MASK_STRICT;
+	bat->notif.event.flags = SSAM_EVENT_SEQUENCED;
+
+	bat->psy_desc.name = bat->name;
+	bat->psy_desc.type = POWER_SUPPLY_TYPE_BATTERY;
+	bat->psy_desc.get_property = spwr_battery_get_property;
+
+	INIT_DELAYED_WORK(&bat->update_work, spwr_battery_update_bst_workfn);
+}
+
+static int spwr_battery_register(struct spwr_battery_device *bat)
+{
+	struct power_supply_config psy_cfg = {};
+	__le32 sta;
+	int status;
+
+	/* Make sure the device is there and functioning properly. */
+	status = ssam_retry(ssam_bat_get_sta, bat->sdev, &sta);
+	if (status)
+		return status;
+
+	if ((le32_to_cpu(sta) & SAM_BATTERY_STA_OK) != SAM_BATTERY_STA_OK)
+		return -ENODEV;
+
+	/* Satisfy lockdep although we are in an exclusive context here. */
+	mutex_lock(&bat->lock);
+
+	status = spwr_battery_update_bix_unlocked(bat);
+	if (status) {
+		mutex_unlock(&bat->lock);
+		return status;
+	}
+
+	if (spwr_battery_present(bat)) {
+		u32 cap_warn = get_unaligned_le32(&bat->bix.design_cap_warn);
+
+		status = spwr_battery_set_alarm_unlocked(bat, cap_warn);
+		if (status) {
+			mutex_unlock(&bat->lock);
+			return status;
+		}
+	}
+
+	mutex_unlock(&bat->lock);
+
+	bat->psy_desc.external_power_changed = spwr_external_power_changed;
+
+	switch (get_unaligned_le32(&bat->bix.power_unit)) {
+	case SAM_BATTERY_POWER_UNIT_mW:
+		bat->psy_desc.properties = spwr_battery_props_eng;
+		bat->psy_desc.num_properties = ARRAY_SIZE(spwr_battery_props_eng);
+		break;
+
+	case SAM_BATTERY_POWER_UNIT_mA:
+		bat->psy_desc.properties = spwr_battery_props_chg;
+		bat->psy_desc.num_properties = ARRAY_SIZE(spwr_battery_props_chg);
+		break;
+
+	default:
+		dev_err(&bat->sdev->dev, "unsupported battery power unit: %u\n",
+			get_unaligned_le32(&bat->bix.power_unit));
+		return -EINVAL;
+	}
+
+	psy_cfg.drv_data = bat;
+	psy_cfg.attr_grp = spwr_battery_groups;
+
+	bat->psy = devm_power_supply_register(&bat->sdev->dev, &bat->psy_desc, &psy_cfg);
+	if (IS_ERR(bat->psy))
+		return PTR_ERR(bat->psy);
+
+	return ssam_notifier_register(bat->sdev->ctrl, &bat->notif);
+}
+
+
+/* -- Driver setup. --------------------------------------------------------- */
+
+static int __maybe_unused surface_battery_resume(struct device *dev)
+{
+	return spwr_battery_recheck_full(dev_get_drvdata(dev));
+}
+SIMPLE_DEV_PM_OPS(surface_battery_pm_ops, NULL, surface_battery_resume);
+
+static int surface_battery_probe(struct ssam_device *sdev)
+{
+	const struct spwr_psy_properties *p;
+	struct spwr_battery_device *bat;
+
+	p = ssam_device_get_match_data(sdev);
+	if (!p)
+		return -ENODEV;
+
+	bat = devm_kzalloc(&sdev->dev, sizeof(*bat), GFP_KERNEL);
+	if (!bat)
+		return -ENOMEM;
+
+	spwr_battery_init(bat, sdev, p->registry, p->name);
+	ssam_device_set_drvdata(sdev, bat);
+
+	return spwr_battery_register(bat);
+}
+
+static void surface_battery_remove(struct ssam_device *sdev)
+{
+	struct spwr_battery_device *bat = ssam_device_get_drvdata(sdev);
+
+	ssam_notifier_unregister(sdev->ctrl, &bat->notif);
+	cancel_delayed_work_sync(&bat->update_work);
+}
+
+static const struct spwr_psy_properties spwr_psy_props_bat1 = {
+	.name = "BAT1",
+	.registry = SSAM_EVENT_REGISTRY_SAM,
+};
+
+static const struct spwr_psy_properties spwr_psy_props_bat2_sb3 = {
+	.name = "BAT2",
+	.registry = SSAM_EVENT_REGISTRY_KIP,
+};
+
+static const struct ssam_device_id surface_battery_match[] = {
+	{ SSAM_SDEV(BAT, 0x01, 0x01, 0x00), (unsigned long)&spwr_psy_props_bat1     },
+	{ SSAM_SDEV(BAT, 0x02, 0x01, 0x00), (unsigned long)&spwr_psy_props_bat2_sb3 },
+	{ },
+};
+MODULE_DEVICE_TABLE(ssam, surface_battery_match);
+
+static struct ssam_device_driver surface_battery_driver = {
+	.probe = surface_battery_probe,
+	.remove = surface_battery_remove,
+	.match_table = surface_battery_match,
+	.driver = {
+		.name = "surface_battery",
+		.pm = &surface_battery_pm_ops,
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
+};
+module_ssam_device_driver(surface_battery_driver);
+
+MODULE_AUTHOR("Maximilian Luz <luzmaximilian@gmail.com>");
+MODULE_DESCRIPTION("Battery driver for Surface System Aggregator Module");
+MODULE_LICENSE("GPL");