bq27xxx: add voltage min design for bq27000 and bq27200

The bq27x00 gauges have an EEPROM register which contains the value of
the voltage that should be considered to be zero battery capacity. Expose
this to userspace using the VOLTAGE_MIN_DESIGN property.

Tested on Nokia N900 with bq27200.

Signed-off-by: Sicelo A. Mhlongo <[email protected]>
Acked-by: Pali Rohár <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sebastian Reichel <[email protected]>

Author: sicelo

drivers/power/supply/bq27xxx_battery.c

@@ -123,6 +123,7 @@ enum bq27xxx_reg_index {
 	BQ27XXX_DM_BLOCK,	/* Data Block */
 	BQ27XXX_DM_DATA,	/* Block Data */
 	BQ27XXX_DM_CKSUM,	/* Block Data Checksum */
+	BQ27XXX_REG_SEDVF,	/* End-of-discharge Voltage */
 	BQ27XXX_REG_MAX,	/* sentinel */
 };
 
@@ -159,6 +160,7 @@ static u8
 		[BQ27XXX_DM_BLOCK] = INVALID_REG_ADDR,
 		[BQ27XXX_DM_DATA] = INVALID_REG_ADDR,
 		[BQ27XXX_DM_CKSUM] = INVALID_REG_ADDR,
+		[BQ27XXX_REG_SEDVF] = 0x77,
 	},
 	bq27010_regs[BQ27XXX_REG_MAX] = {
 		[BQ27XXX_REG_CTRL] = 0x00,
@@ -184,6 +186,7 @@ static u8
 		[BQ27XXX_DM_BLOCK] = INVALID_REG_ADDR,
 		[BQ27XXX_DM_DATA] = INVALID_REG_ADDR,
 		[BQ27XXX_DM_CKSUM] = INVALID_REG_ADDR,
+		[BQ27XXX_REG_SEDVF] = 0x77,
 	},
 	bq2750x_regs[BQ27XXX_REG_MAX] = {
 		[BQ27XXX_REG_CTRL] = 0x00,
@@ -579,6 +582,7 @@ static enum power_supply_property bq27000_props[] = {
 	POWER_SUPPLY_PROP_POWER_AVG,
 	POWER_SUPPLY_PROP_HEALTH,
 	POWER_SUPPLY_PROP_MANUFACTURER,
+	POWER_SUPPLY_PROP_VOLTAGE_MIN_DESIGN,
 };
 
 static enum power_supply_property bq27010_props[] = {
@@ -599,6 +603,7 @@ static enum power_supply_property bq27010_props[] = {
 	POWER_SUPPLY_PROP_CYCLE_COUNT,
 	POWER_SUPPLY_PROP_HEALTH,
 	POWER_SUPPLY_PROP_MANUFACTURER,
+	POWER_SUPPLY_PROP_VOLTAGE_MIN_DESIGN,
 };
 
 #define bq2750x_props bq27510g3_props
@@ -2039,6 +2044,36 @@ static int bq27xxx_battery_voltage(struct bq27xxx_device_info *di,
 	return 0;
 }
 
+/*
+ * Return the design minimum battery Voltage in microvolts
+ * Or < 0 if something fails.
+ */
+static int bq27xxx_battery_read_dmin_volt(struct bq27xxx_device_info *di,
+					  union power_supply_propval *val)
+{
+	int volt;
+
+	/* We only have to read design minimum voltage once */
+	if (di->voltage_min_design > 0) {
+		val->intval = di->voltage_min_design;
+		return 0;
+	}
+
+	volt = bq27xxx_read(di, BQ27XXX_REG_SEDVF, true);
+	if (volt < 0) {
+		dev_err(di->dev, "error reading design min voltage\n");
+		return volt;
+	}
+
+	/* SEDVF = Design EDVF / 8 - 256 */
+	val->intval = volt * 8000 + 2048000;
+
+	/* Save for later reads */
+	di->voltage_min_design = val->intval;
+
+	return 0;
+}
+
 static int bq27xxx_simple_value(int value,
 				union power_supply_propval *val)
 {
@@ -2119,8 +2154,10 @@ static int bq27xxx_battery_get_property(struct power_supply *psy,
 	 * power_supply_battery_info visible in sysfs.
 	 */
 	case POWER_SUPPLY_PROP_ENERGY_FULL_DESIGN:
-	case POWER_SUPPLY_PROP_VOLTAGE_MIN_DESIGN:
 		return -EINVAL;
+	case POWER_SUPPLY_PROP_VOLTAGE_MIN_DESIGN:
+		ret = bq27xxx_battery_read_dmin_volt(di, val);
+		break;
 	case POWER_SUPPLY_PROP_CYCLE_COUNT:
 		ret = bq27xxx_battery_read_cyct(di, val);
 		break;

include/linux/power/bq27xxx_battery.h

@@ -61,6 +61,7 @@ struct bq27xxx_device_info {
 	struct bq27xxx_access_methods bus;
 	struct bq27xxx_reg_cache cache;
 	int charge_design_full;
+	int voltage_min_design;
 	bool removed;
 	unsigned long last_update;
 	union power_supply_propval last_status;