clocksource: Add 'max_cycles' to 'struct clocksource'

In order to facilitate clocksource validation, add a
'max_cycles' field to the clocksource structure which
will hold the maximum cycle value that can safely be
multiplied without potentially causing an overflow.

Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1426133800-29329-4-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 3 insertions, 2 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);