power: supply: bq27xxx: do not report bogus zero values

On the bq27x00 and bq27x10 variants, a number of conditions may reset the value
stored in the NAC register. This will cause capacity, energy, and charge to
report the value 0, even when the battery is full. On the other hand, the chip
also provides a flag, EDVF, which accurately detects the true battery empty
condition, when capacity, charge, and energy are really 0.  Therefore, discard
readings for these properties if their value is 0 while EDVF is unset.

Tested on the Nokia N900 with bq27200.

Signed-off-by: Sicelo A. Mhlongo <absicsz@gmail.com>
Link: https://lore.kernel.org/r/20250207220605.106768-1-absicsz@gmail.com
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Author: sicelo

drivers/power/supply/bq27xxx_battery.c

@@ -2149,6 +2149,10 @@ static int bq27xxx_battery_get_property(struct power_supply *psy,
 		break;
 	case POWER_SUPPLY_PROP_CAPACITY:
 		ret = bq27xxx_simple_value(di->cache.capacity, val);
+		/* If 0 is reported, it is expected that EDVF is also set */
+		if (!ret && di->opts & BQ27XXX_O_ZERO &&
+		   !(di->cache.flags & BQ27000_FLAG_EDVF))
+			return -EINVAL;
 		break;
 	case POWER_SUPPLY_PROP_CAPACITY_LEVEL:
 		ret = bq27xxx_battery_capacity_level(di, val);
@@ -2172,10 +2176,15 @@ static int bq27xxx_battery_get_property(struct power_supply *psy,
 			val->intval = POWER_SUPPLY_TECHNOLOGY_LION;
 		break;
 	case POWER_SUPPLY_PROP_CHARGE_NOW:
-		if (di->regs[BQ27XXX_REG_NAC] != INVALID_REG_ADDR)
+		if (di->regs[BQ27XXX_REG_NAC] != INVALID_REG_ADDR) {
 			ret = bq27xxx_battery_read_nac(di, val);
-		else
+			/* If 0 is reported, it is expected that EDVF is also set */
+			if (!ret && di->opts & BQ27XXX_O_ZERO &&
+			   !(di->cache.flags & BQ27000_FLAG_EDVF))
+				return -EINVAL;
+		} else {
 			ret = bq27xxx_battery_read_rc(di, val);
+		}
 		break;
 	case POWER_SUPPLY_PROP_CHARGE_FULL:
 		ret = bq27xxx_battery_read_fcc(di, val);
@@ -2200,6 +2209,10 @@ static int bq27xxx_battery_get_property(struct power_supply *psy,
 		break;
 	case POWER_SUPPLY_PROP_ENERGY_NOW:
 		ret = bq27xxx_battery_read_energy(di, val);
+		/* If 0 is reported, it is expected that EDVF is also set */
+		if (!ret && di->opts & BQ27XXX_O_ZERO &&
+		   !(di->cache.flags & BQ27000_FLAG_EDVF))
+			return -EINVAL;
 		break;
 	case POWER_SUPPLY_PROP_POWER_AVG:
 		ret = bq27xxx_battery_pwr_avg(di, val);