time/timecounter: Fix inline documentation

Fix kernel-doc warnings, text punctuation, and a kernel-doc marker
(change '%' to '&' to indicate a struct):

  timecounter.h:72: warning: No description found for return value of 'cyclecounter_cyc2ns'
  timecounter.h:85: warning: Function parameter or member 'tc' not described in 'timecounter_adjtime'
  timecounter.h:111: warning: No description found for return value of 'timecounter_read'
  timecounter.h:128: warning: No description found for return value of 'timecounter_cyc2time'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240331172652.14086-2-rdunlap@infradead.org

Author: rddunlap

include/linux/timecounter.h

@@ -22,7 +22,7 @@
  *
  * @read:		returns the current cycle value
  * @mask:		bitmask for two's complement
- *			subtraction of non 64 bit counters,
+ *			subtraction of non-64-bit counters,
  *			see CYCLECOUNTER_MASK() helper macro
  * @mult:		cycle to nanosecond multiplier
  * @shift:		cycle to nanosecond divisor (power of two)
@@ -35,7 +35,7 @@ struct cyclecounter {
 };
 
 /**
- * struct timecounter - layer above a %struct cyclecounter which counts nanoseconds
+ * struct timecounter - layer above a &struct cyclecounter which counts nanoseconds
  *	Contains the state needed by timecounter_read() to detect
  *	cycle counter wrap around. Initialize with
  *	timecounter_init(). Also used to convert cycle counts into the
@@ -66,6 +66,8 @@ struct timecounter {
  * @cycles:	Cycles
  * @mask:	bit mask for maintaining the 'frac' field
  * @frac:	pointer to storage for the fractional nanoseconds.
+ *
+ * Returns: cycle counter cycles converted to nanoseconds
  */
 static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc,
 				      u64 cycles, u64 mask, u64 *frac)
@@ -79,6 +81,7 @@ static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc,
 
 /**
  * timecounter_adjtime - Shifts the time of the clock.
+ * @tc:		The &struct timecounter to adjust
  * @delta:	Desired change in nanoseconds.
  */
 static inline void timecounter_adjtime(struct timecounter *tc, s64 delta)
@@ -107,6 +110,8 @@ extern void timecounter_init(struct timecounter *tc,
  *
  * In other words, keeps track of time since the same epoch as
  * the function which generated the initial time stamp.
+ *
+ * Returns: nanoseconds since the initial time stamp
  */
 extern u64 timecounter_read(struct timecounter *tc);
 
@@ -123,6 +128,8 @@ extern u64 timecounter_read(struct timecounter *tc);
  *
  * This allows conversion of cycle counter values which were generated
  * in the past.
+ *
+ * Returns: cycle counter converted to nanoseconds since the initial time stamp
  */
 extern u64 timecounter_cyc2time(const struct timecounter *tc,
 				u64 cycle_tstamp);