[PATCH] bq27xxx: add voltage min design for bq27000 and bq27200

["Sicelo A. Mhlongo" <absicsz@gmail.com>]

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 <absicsz@gmail.com>
---
 drivers/power/supply/bq27xxx_battery.c | 39 +++++++++++++++++++++++++-
 include/linux/power/bq27xxx_battery.h  |  1 +
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/drivers/power/supply/bq27xxx_battery.c b/drivers/power/supply/bq27xxx_battery.c
index 40c5ac7a1118..90a5bccfc6b9 100644
--- a/drivers/power/supply/bq27xxx_battery.c
+++ b/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;
diff --git a/include/linux/power/bq27xxx_battery.h b/include/linux/power/bq27xxx_battery.h
index 5180dc9f1706..6b190639b08e 100644
--- a/include/linux/power/bq27xxx_battery.h
+++ b/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;
-- 
2.45.2