[PATCH] power: supply: add stubs for notifier registration helpers

[Elson Serrao]

power_supply_reg_notifier() and power_supply_unreg_notifier() are declared
unconditionally, with no fallback when CONFIG_POWER_SUPPLY is disabled.
Any driver that calls them unconditionally fails to link:

ERROR: modpost: "power_supply_unreg_notifier" [drivers/usb/dwc3/dwc3.ko]
undefined!
ERROR: modpost: "power_supply_reg_notifier" [drivers/usb/dwc3/dwc3.ko]
undefined!

Fix this by adding stub functions for these calls.

Fixes: 7c87ef27af79 ("usb: dwc3: avoid probe deferral when USB power supply is not available")
Reported-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Closes: https://lore.kernel.org/all/a9dd53b3-0666-404a-99e0-76617ae3f944@xxxxxxxxxxxxx/
Signed-off-by: Elson Serrao <elson.serrao@xxxxxxxxxxxxxxxx>
---
 include/linux/power_supply.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/power_supply.h b/include/linux/power_supply.h
index a9c056f13077..e749d2189335 100644
--- a/include/linux/power_supply.h
+++ b/include/linux/power_supply.h
@@ -816,15 +816,18 @@ struct power_supply_battery_info {
 	int bti_resistance_tolerance;
 };
 
+#if IS_ENABLED(CONFIG_POWER_SUPPLY)
 extern int power_supply_reg_notifier(struct notifier_block *nb);
 extern void power_supply_unreg_notifier(struct notifier_block *nb);
-#if IS_ENABLED(CONFIG_POWER_SUPPLY)
 extern struct power_supply *power_supply_get_by_name(const char *name);
 extern int __must_check power_supply_get_system_batteries(struct device *dev,
 							  struct power_supply ***psys);
 extern void power_supply_put_system_batteries(struct power_supply **psys, int count);
 extern void power_supply_put(struct power_supply *psy);
 #else
+static inline int power_supply_reg_notifier(struct notifier_block *nb)
+{ return -EOPNOTSUPP; }
+static inline void power_supply_unreg_notifier(struct notifier_block *nb) {}
 static inline void power_supply_put(struct power_supply *psy) {}
 static inline struct power_supply *power_supply_get_by_name(const char *name)
 { return NULL; }
-- 
2.34.1