To initialize hrtimer, hrtimer_init() needs to be called and also
hrtimer::function must be set. This is error-prone and awkward to use.

Introduce hrtimer_setup() which does both of these things, so that users of
hrtimer can be simplified.

The new setup function also has a sanity check for the provided function
pointer. If NULL, a warning is emitted and a dummy callback installed.

hrtimer_init() will be removed as soon as all of its users have been
converted to the new function.

Signed-off-by: Nam Cao <namcao@linutronix.de>
---
 include/linux/hrtimer.h |  2 ++
 kernel/time/hrtimer.c   | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 5aa9d57528c4..bcc0715c59a8 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -228,6 +228,8 @@ static inline void hrtimer_cancel_wait_running(struct hrtimer *timer)
 /* Initialize timers: */
 extern void hrtimer_init(struct hrtimer *timer, clockid_t which_clock,
 			 enum hrtimer_mode mode);
+extern void hrtimer_setup(struct hrtimer *timer, enum hrtimer_restart (*function)(struct hrtimer *),
+			  clockid_t clock_id, enum hrtimer_mode mode);
 extern void hrtimer_init_on_stack(struct hrtimer *timer, clockid_t which_clock,
 				  enum hrtimer_mode mode);
 extern void hrtimer_init_sleeper_on_stack(struct hrtimer_sleeper *sl,
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 4b0507cf38ea..a5ef67edcda9 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1535,6 +1535,11 @@ static inline int hrtimer_clockid_to_base(clockid_t clock_id)
 	return HRTIMER_BASE_MONOTONIC;
 }
 
+static enum hrtimer_restart hrtimer_dummy_timeout(struct hrtimer *unused)
+{
+	return HRTIMER_NORESTART;
+}
+
 static void __hrtimer_init(struct hrtimer *timer, clockid_t clock_id,
 			   enum hrtimer_mode mode)
 {
@@ -1571,6 +1576,18 @@ static void __hrtimer_init(struct hrtimer *timer, clockid_t clock_id,
 	timerqueue_init(&timer->node);
 }
 
+static void __hrtimer_setup(struct hrtimer *timer,
+			    enum hrtimer_restart (*function)(struct hrtimer *),
+			    clockid_t clock_id, enum hrtimer_mode mode)
+{
+	__hrtimer_init(timer, clock_id, mode);
+
+	if (WARN_ON_ONCE(!function))
+		timer->function = hrtimer_dummy_timeout;
+	else
+		timer->function = function;
+}
+
 /**
  * hrtimer_init - initialize a timer to the given clock
  * @timer:	the timer to be initialized
@@ -1591,6 +1608,27 @@ void hrtimer_init(struct hrtimer *timer, clockid_t clock_id,
 }
 EXPORT_SYMBOL_GPL(hrtimer_init);
 
+/**
+ * hrtimer_setup - initialize a timer to the given clock
+ * @timer:	the timer to be initialized
+ * @function:	the callback function
+ * @clock_id:	the clock to be used
+ * @mode:       The modes which are relevant for initialization:
+ *              HRTIMER_MODE_ABS, HRTIMER_MODE_REL, HRTIMER_MODE_ABS_SOFT,
+ *              HRTIMER_MODE_REL_SOFT
+ *
+ *              The PINNED variants of the above can be handed in,
+ *              but the PINNED bit is ignored as pinning happens
+ *              when the hrtimer is started
+ */
+void hrtimer_setup(struct hrtimer *timer, enum hrtimer_restart (*function)(struct hrtimer *),
+		   clockid_t clock_id, enum hrtimer_mode mode)
+{
+	debug_init(timer, clock_id, mode);
+	__hrtimer_setup(timer, function, clock_id, mode);
+}
+EXPORT_SYMBOL_GPL(hrtimer_setup);
+
 /**
  * hrtimer_init_on_stack - initialize a timer in stack memory
  * @timer:	The timer to be initialized
-- 
2.39.5