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@???>
---
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