In order to facilitate some clocksource validation,
add a max_cycles entry to the structure which will
hold the maximum cycle value that can safely be
multiplied without potentially causing an overflow.
Cc: Dave Jones <da...@codemonkey.org.uk>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Richard Cochran <richardcoch...@gmail.com>
Cc: Prarit Bhargava <pra...@redhat.com>
Cc: Stephen Boyd <sb...@codeaurora.org>
Cc: Ingo Molnar <mi...@kernel.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Signed-off-by: John Stultz <john.stu...@linaro.org>
---
include/linux/clocksource.h | 6 ++++--
kernel/time/clocksource.c | 15 ++++++++++++---
kernel/time/sched_clock.c | 2 +-
3 files changed, 17 insertions(+), 6 deletions(-)
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 9c78d15..63fe52f 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 mult
* @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 +190,8 @@ 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 4988411..e6c752b 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -469,11 +469,14 @@ 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 saftey margin)
*
* NOTE: This function includes a saftey 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 +496,10 @@ 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;
@@ -671,7 +678,8 @@ void __clocksource_updatefreq_scale(struct clocksource *cs,
u32 scale, u32 freq)
}
cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
- cs->maxadj, cs->mask);
+ cs->maxadj, cs->mask,
+ &cs->max_cycles);
}
EXPORT_SYMBOL_GPL(__clocksource_updatefreq_scale);
@@ -719,7 +727,8 @@ int clocksource_register(struct clocksource *cs)
/* calculate max idle time permitted for this clocksource */
cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
- cs->maxadj, cs->mask);
+ cs->maxadj, cs->mask,
+ &cs->max_cycles);
mutex_lock(&clocksource_mutex);
clocksource_enqueue(cs);
diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
index c794b84..d43855b 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 ns 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*/
--
1.9.1
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