power: supply: axp288_fuelguage: Do not bind when the fg function is not used

Some devices with an AXP288 PMIC do not have a battery at all, or use
external charger and fuelgauge ICs instead of the AXP288 builtin
functionality.

On such devices we should not bind to the fuelgauge function to avoid
exporting a non working power_supply class device.

This also avoids the following errors repeating over and over again in
dmesg:

axp288_fuel_gauge axp288_fuel_gauge: capacity measurement not valid
axp288_fuel_gauge axp288_fuel_gauge: Error 0xe2 contents not valid
power_supply axp288_fuel_gauge: driver failed to report 'charge_now'
property: -6

Cc: Carlo Caione <carlo@endlessm.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>

drivers/power/supply/axp288_fuel_gauge.c

@@ -754,10 +754,21 @@ static int axp288_fuel_gauge_probe(struct platform_device *pdev)
 		[BAT_D_CURR] = "axp288-chrg-d-curr",
 		[BAT_VOLT] = "axp288-batt-volt",
 	};
+	unsigned int val;
 
 	if (dmi_check_system(axp288_fuel_gauge_blacklist))
 		return -ENODEV;
 
+	/*
+	 * On some devices the fuelgauge and charger parts of the axp288 are
+	 * not used, check that the fuelgauge is enabled (CC_CTRL != 0).
+	 */
+	ret = regmap_read(axp20x->regmap, AXP20X_CC_CTRL, &val);
+	if (ret < 0)
+		return ret;
+	if (val == 0)
+		return -ENODEV;
+
 	info = devm_kzalloc(&pdev->dev, sizeof(*info), GFP_KERNEL);
 	if (!info)
 		return -ENOMEM;