power: supply: axp288_fuel_gauge: Only read PWR_OP_MODE, FG_LOW_CAP_REG regs once

Accessing registers on the AXP288 is quite expensive, so we should avoid
doing unnecessary accesses.

The FG_LOW_CAP_REG never changes underneath us, so we only need to read
it once. Devices with an AXP288 do not have user-replace (let alone
hot-swappable) batteries and the only bit we care about in the
PWR_OP_MODE register is the CHRG_STAT_BAT_PRESENT bit, so we can get
away with only reading the PWR_OP_MODE register once too.

Note that the FG_LOW_CAP_REG is not marked volatile in the regmap, so we
were effectively already reading it once. This change makes this explicit,
this is done as preparation of a further patch which moves all remaining
register accesses in fuel_gauge_get_property() out of that function.

Signed-off-by: Hans de Goede <[e-mail]>
Signed-off-by: Sebastian Reichel <[e-mail]>

drivers/power/supply/axp288_fuel_gauge.c

···
 	struct mutex lock;
 	int status;
 	int max_volt;
+	int pwr_op;
+	int low_cap;
 	struct dentry *debug_file;
 };
 
···
 		val->intval = PROP_CURR(value);
 		break;
 	case POWER_SUPPLY_PROP_PRESENT:
-		ret = fuel_gauge_reg_readb(info, AXP20X_PWR_OP_MODE);
-		if (ret < 0)
-			goto fuel_gauge_read_err;
-
-		if (ret & CHRG_STAT_BAT_PRESENT)
+		if (info->pwr_op & CHRG_STAT_BAT_PRESENT)
 			val->intval = 1;
 		else
 			val->intval = 0;
···
 		val->intval = (ret & FG_REP_CAP_VAL_MASK);
 		break;
 	case POWER_SUPPLY_PROP_CAPACITY_ALERT_MIN:
-		ret = fuel_gauge_reg_readb(info, AXP288_FG_LOW_CAP_REG);
-		if (ret < 0)
-			goto fuel_gauge_read_err;
-		val->intval = (ret & 0x0f);
+		val->intval = (info->low_cap & 0x0f);
 		break;
 	case POWER_SUPPLY_PROP_TECHNOLOGY:
 		val->intval = POWER_SUPPLY_TECHNOLOGY_LION;
···
 		const union power_supply_propval *val)
 {
 	struct axp288_fg_info *info = power_supply_get_drvdata(ps);
-	int ret = 0;
+	int new_low_cap, ret = 0;
 
 	mutex_lock(&info->lock);
 	switch (prop) {
···
 			ret = -EINVAL;
 			break;
 		}
-		ret = fuel_gauge_reg_readb(info, AXP288_FG_LOW_CAP_REG);
-		if (ret < 0)
-			break;
-		ret &= 0xf0;
-		ret |= (val->intval & 0xf);
-		ret = fuel_gauge_reg_writeb(info, AXP288_FG_LOW_CAP_REG, ret);
+		new_low_cap = info->low_cap;
+		new_low_cap &= 0xf0;
+		new_low_cap |= (val->intval & 0xf);
+		ret = fuel_gauge_reg_writeb(info, AXP288_FG_LOW_CAP_REG, new_low_cap);
+		if (ret == 0)
+			info->low_cap = new_low_cap;
 		break;
 	default:
 		ret = -EINVAL;
···
 		info->max_volt = 4350;
 		break;
 	}
+
+	ret = fuel_gauge_reg_readb(info, AXP20X_PWR_OP_MODE);
+	if (ret < 0)
+		goto out_free_iio_chan;
+	info->pwr_op = ret;
+
+	ret = fuel_gauge_reg_readb(info, AXP288_FG_LOW_CAP_REG);
+	if (ret < 0)
+		goto out_free_iio_chan;
+	info->low_cap = ret;
 
 	psy_cfg.drv_data = info;
 	info->bat = power_supply_register(&pdev->dev, &fuel_gauge_desc, &psy_cfg);