clocksource: Add devm_clocksource_register_*() helpers

Introduce device-managed helpers for clocksource registration.

The clocksource framework currently provides __clocksource_register_scale()
along with convenience wrappers for Hz and kHz registration. However,
drivers must handle error paths and cleanup manually, typically by pairing
registration with an explicit clocksource_unregister() call.

Add a devm-based variant, __devm_clocksource_register_scale(), along with
devm_clocksource_register_hz() and devm_clocksource_register_khz() helpers.

These helpers register the clocksource and attach a devres action to
automatically unregister it on driver detach or probe failure.

This simplifies driver code by:

  * removing explicit cleanup paths
  * ensuring correct teardown ordering
  * aligning with the devm-based resource management model widely used
    across the kernel

While drivers can open-code devm_add_action_or_reset(), providing a
dedicated helper avoids duplication, reduces boilerplate, and ensures
consistent usage across drivers, following patterns used in other
subsystems.

This is also particularly useful for drivers built as modules, where
device-managed resource handling avoids manual cleanup in remove paths and
ensures correct teardown on module unload.

This helper is self-contained and can be adopted progressively by drivers.

No functional change.

Signed-off-by: Daniel Lezcano <daniel.lezcano@oss.qualcomm.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260506153831.605159-1-daniel.lezcano@oss.qualcomm.com

include/linux/clocksource.h

@@ -236,6 +236,9 @@ clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 minsec);
  */
 extern int
 __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq);
+extern int
+__devm_clocksource_register_scale(struct device *dev, struct clocksource *cs,
+				  u32 scale, u32 freq);
 extern void
 __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq);
 
@@ -258,6 +261,18 @@ static inline int clocksource_register_khz(struct clocksource *cs, u32 khz)
 	return __clocksource_register_scale(cs, 1000, khz);
 }
 
+static inline int devm_clocksource_register_hz(struct device *dev,
+					       struct clocksource *cs, u32 hz)
+{
+	return __devm_clocksource_register_scale(dev, cs, 1, hz);
+}
+
+static inline int devm_clocksource_register_khz(struct device *dev,
+						struct clocksource *cs, u32 khz)
+{
+	return __devm_clocksource_register_scale(dev, cs, 1000, khz);
+}
+
 static inline void __clocksource_update_freq_hz(struct clocksource *cs, u32 hz)
 {
 	__clocksource_update_freq_scale(cs, 1, hz);

kernel/time/clocksource.c

@@ -1338,6 +1338,26 @@ int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
 }
 EXPORT_SYMBOL_GPL(__clocksource_register_scale);
 
+static void __devm_clocksource_unregister(void *data)
+{
+	struct clocksource *cs = data;
+
+	clocksource_unregister(cs);
+}
+
+int __devm_clocksource_register_scale(struct device *dev, struct clocksource *cs,
+				      u32 scale, u32 freq)
+{
+	int ret;
+
+	ret = __clocksource_register_scale(cs, scale, freq);
+	if (ret)
+		return ret;
+
+	return devm_add_action_or_reset(dev, __devm_clocksource_unregister, cs);
+}
+EXPORT_SYMBOL_GPL(__devm_clocksource_register_scale);
+
 /*
  * Unbind clocksource @cs. Called with clocksource_mutex held
  */