HACK: power: supply: pm8916_bms_vm: Add a basic voltage based SOC filter

Unfortunately, VM-BMS provides literally nothing but the voltage to
guess the state of charge (SOC). Add some crude guesstimation algorithm
for now so the devices don't just turn off because userspace is unable
to detect the remaining battery capacity.

Signed-off-by: Nikita Travkin <[email protected]>

drivers/power/supply/pm8916_bms_vm.c

@@ -53,6 +53,7 @@ struct pm8916_bms_vm_battery {
 	unsigned int last_ocv;
 	time64_t last_ocv_time;
 	unsigned int vbat_now;
+	unsigned int fake_ocv;
 };
 
 static int pm8916_bms_vm_battery_get_property(struct power_supply *psy,
@@ -84,6 +85,10 @@ static int pm8916_bms_vm_battery_get_property(struct power_supply *psy,
 			val->intval = POWER_SUPPLY_HEALTH_GOOD;
 		return 0;
 
+	case POWER_SUPPLY_PROP_CAPACITY:
+		val->intval = power_supply_batinfo_ocv2cap(info, bat->fake_ocv, 20);
+		return 0;
+
 	case POWER_SUPPLY_PROP_VOLTAGE_NOW:
 		val->intval = bat->vbat_now;
 		return 0;
@@ -109,28 +114,75 @@ static enum power_supply_property pm8916_bms_vm_battery_properties[] = {
 	POWER_SUPPLY_PROP_VOLTAGE_NOW,
 	POWER_SUPPLY_PROP_VOLTAGE_OCV,
 	POWER_SUPPLY_PROP_HEALTH,
+	POWER_SUPPLY_PROP_CAPACITY,
 };
 
 static irqreturn_t pm8916_bms_vm_fifo_update_done_irq(int irq, void *data)
 {
 	struct pm8916_bms_vm_battery *bat = data;
+	struct power_supply_battery_info *info = bat->info;
 	u16 vbat_data[PM8916_BMS_VM_FIFO_COUNT];
-	int ret;
+	int i, ret, delta = 0, loc_delta;
+	unsigned int tmp = 0;
+	int supplied;
 
 	ret = regmap_bulk_read(bat->regmap, bat->reg + PM8916_BMS_VM_BMS_FIFO_REG_0_LSB,
 			       &vbat_data, PM8916_BMS_VM_FIFO_COUNT * 2);
 	if (ret)
 		return IRQ_HANDLED;
 
+	/* We assume that we don't charge if no charger is present */
+	supplied = power_supply_am_i_supplied(bat->battery);
+	if (supplied == -ENODEV)
+		supplied = 0;
+	else if (supplied < 0)
+		return IRQ_HANDLED;
+
+	for (i = 0; i < PM8916_BMS_VM_FIFO_COUNT; i++) {
+		tmp = vbat_data[i] * 300 - 100000;
+
+		loc_delta = tmp - bat->vbat_now;
+		delta += loc_delta;
+		bat->vbat_now = tmp;
+	}
+
 	/*
 	 * The VM-BMS hardware only collects voltage data and the software
 	 * has to process it to calculate the OCV and SoC. Hardware provides
 	 * up to 8 averaged measurements for software to take in account.
 	 *
-	 * Just use the last measured value for now to report the current
-	 * battery voltage.
+	 * NOTE: Since VM-BMS is mostly implemented in software, OCV needs to be estimated.
+	 * This driver makes some assumptions to estimate OCV from averaged VBAT measurements
+	 * and initial OCV measurements taken on boot or while in suspend:
+	 *
+	 *  - When charger is online, ocv can only increase.
+	 *  - When charger is offline, ocv can only decrease and ocv > vbat.
+	 *  - ocv can't change more than 0.025v between the measurements.
+	 *  - When charger is in CV mode (vbat = const vbat-max), ocv increases by
+	 *    0.004v every measurement until it reaches vbat.
+	 *
+	 * Those assumptions give somewhat realistic estimation of ocv and capacity, though
+	 * in some worst case scenarios it will perform poorly.
+	 * Ideally proper BMS algorithm should be implemented in userspace.
 	 */
-	bat->vbat_now = vbat_data[PM8916_BMS_VM_FIFO_COUNT - 1] * 300;
+
+	if ((supplied && delta > 0) || (!supplied && delta < 0))
+		if (abs(delta) < 25000) /* 0.025v */
+			bat->fake_ocv += delta;
+
+	if (!supplied && bat->fake_ocv < bat->vbat_now)
+		bat->fake_ocv = bat->vbat_now;
+
+	regmap_write(bat->regmap, bat->reg + PM8916_BMS_VM_STATUS1, 0);
+	regmap_read(bat->regmap, bat->reg + PM8916_BMS_VM_STATUS1, &tmp);
+
+	if (PM8916_BMS_VM_FSM_STATE(tmp) == PM8916_BMS_VM_FSM_STATE_S2 &&
+	    bat->fake_ocv < bat->vbat_now - 10000 /* 0.01v */) {
+		bat->fake_ocv += 4000; /* 0.004v */
+	}
+
+	if (supplied && bat->fake_ocv > info->voltage_max_design_uv)
+		bat->fake_ocv = info->voltage_max_design_uv;
 
 	power_supply_changed(bat->battery);
 
@@ -208,6 +260,7 @@ static int pm8916_bms_vm_battery_probe(struct platform_device *pdev)
 	bat->last_ocv_time = ktime_get_seconds();
 	bat->last_ocv = tmp * 300;
 	bat->vbat_now = bat->last_ocv;
+	bat->fake_ocv = bat->last_ocv;
 
 	psy_cfg.drv_data = bat;
 	psy_cfg.of_node = dev->of_node;
@@ -266,6 +319,7 @@ static int pm8916_bms_vm_battery_resume(struct platform_device *pdev)
 
 	bat->last_ocv_time = ktime_get_seconds();
 	bat->last_ocv = tmp * 300;
+	bat->fake_ocv = bat->last_ocv;
 
 	ret = regmap_write(bat->regmap,
 			   bat->reg + PM8916_SEC_ACCESS, PM8916_SEC_MAGIC);