3 files changed, 20 insertions, 15 deletions

diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 9c78d15d33e4..16d048cadebb 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -56,6 +56,7 @@ struct module;
  * @shift:              cycle to nanosecond divisor (power of two)
  * @max_idle_ns:        max idle time permitted by the clocksource (nsecs)
  * @maxadj:             maximum adjustment value to mult (~11%)
+ * @max_cycles:         maximum safe cycle value which won't overflow on multiplication
  * @flags:              flags describing special properties
  * @archdata:           arch-specific data
  * @suspend:            suspend function for the clocksource, if necessary
@@ -76,7 +77,7 @@ struct clocksource {
 #ifdef CONFIG_ARCH_CLOCKSOURCE_DATA
         struct arch_clocksource_data archdata;
 #endif
-
+        u64 max_cycles;
         const char *name;
         struct list_head list;
         int rating;
@@ -189,7 +190,7 @@ extern struct clocksource * __init clocksource_default_clock(void);
 extern void clocksource_mark_unstable(struct clocksource *cs);
 
 extern u64
-clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask);
+clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cycles);
 extern void
 clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 minsec);
 
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index ace95763b3a6..fc2a9de43ca1 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -469,11 +469,13 @@ static u32 clocksource_max_adjustment(struct clocksource *cs)
  * @shift:      cycle to nanosecond divisor (power of two)
  * @maxadj:     maximum adjustment value to mult (~11%)
  * @mask:       bitmask for two's complement subtraction of non 64 bit counters
+ * @max_cyc:    maximum cycle value before potential overflow (does not include
+ *              any safety margin)
  *
  * NOTE: This function includes a safety margin of 50%, so that bad clock values
  * can be detected.
  */
-u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask)
+u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
 {
         u64 max_nsecs, max_cycles;
 
@@ -493,6 +495,10 @@ u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask)
         max_cycles = min(max_cycles, mask);
         max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);
 
+        /* return the max_cycles value as well if requested */
+        if (max_cyc)
+                *max_cyc = max_cycles;
+
         /* Return 50% of the actual maximum, so we can detect bad values */
         max_nsecs >>= 1;
 
@@ -500,17 +506,15 @@ u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask)
 }
 
 /**
- * clocksource_max_deferment - Returns max time the clocksource should be deferred
- * @cs:         Pointer to clocksource
+ * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles
+ * @cs:         Pointer to clocksource to be updated
  *
  */
-static u64 clocksource_max_deferment(struct clocksource *cs)
+static inline void clocksource_update_max_deferment(struct clocksource *cs)
 {
-        u64 max_nsecs;
-
-        max_nsecs = clocks_calc_max_nsecs(cs->mult, cs->shift, cs->maxadj,
-                                          cs->mask);
-        return max_nsecs;
+        cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
+                                                cs->maxadj, cs->mask,
+                                                &cs->max_cycles);
 }
 
 #ifndef CONFIG_ARCH_USES_GETTIMEOFFSET
@@ -684,7 +688,7 @@ void __clocksource_updatefreq_scale(struct clocksource *cs, u32 scale, u32 freq)
                 cs->maxadj = clocksource_max_adjustment(cs);
         }
 
-        cs->max_idle_ns = clocksource_max_deferment(cs);
+        clocksource_update_max_deferment(cs);
 }
 EXPORT_SYMBOL_GPL(__clocksource_updatefreq_scale);
 
@@ -730,8 +734,8 @@ int clocksource_register(struct clocksource *cs)
                 "Clocksource %s might overflow on 11%% adjustment\n",
                 cs->name);
 
-        /* calculate max idle time permitted for this clocksource */
-        cs->max_idle_ns = clocksource_max_deferment(cs);
+        /* Update max idle time permitted for this clocksource */
+        clocksource_update_max_deferment(cs);
 
         mutex_lock(&clocksource_mutex);
         clocksource_enqueue(cs);
diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
index 3b8ae45020c1..ca3bc5c7027c 100644
--- a/kernel/time/sched_clock.c
+++ b/kernel/time/sched_clock.c
@@ -126,7 +126,7 @@ void __init sched_clock_register(u64 (*read)(void), int bits,
         new_mask = CLOCKSOURCE_MASK(bits);
 
         /* calculate how many nanosecs until we risk wrapping */
-        wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask);
+        wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask, NULL);
         new_wrap_kt = ns_to_ktime(wrap);
 
         /* update epoch for new counter and update epoch_ns from old counter*/