[patch 4/6] timekeeping: Use mul_u64_u32_shr() instead of open coding it

Thomas Gleixner
2016-12-08T20:53:23Z

[-- Attachment #1: timekeeping--Use-mul_u64_u32_shr---instead-of-open-coding-it.patch --]
[-- Type: text/plain, Size: 1806 bytes --]

The resume code must deal with a clocksource delta which is potentially big
enough to overflow the 64bit mult.

Replace the open coded handling with the proper function.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/time/timekeeping.c | 26 +++++---------------------
1 file changed, 5 insertions(+), 21 deletions(-)

--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1615,7 +1615,7 @@ void timekeeping_resume(void)
struct clocksource *clock = tk->tkr_mono.clock;
unsigned long flags;
struct timespec64 ts_new, ts_delta;
- cycle_t cycle_now, cycle_delta;
+ cycle_t cycle_now;

sleeptime_injected = false;
read_persistent_clock64(&ts_new);
@@ -1641,27 +1641,11 @@ void timekeeping_resume(void)
cycle_now = tk->tkr_mono.read(clock);
if ((clock->flags & CLOCK_SOURCE_SUSPEND_NONSTOP) &&
cycle_now > tk->tkr_mono.cycle_last) {
- u64 num, max = ULLONG_MAX;
- u32 mult = clock->mult;
- u32 shift = clock->shift;
- s64 nsec = 0;
-
- cycle_delta = clocksource_delta(cycle_now, tk->tkr_mono.cycle_last,
- tk->tkr_mono.mask);
-
- /*
- * "cycle_delta * mutl" may cause 64 bits overflow, if the
- * suspended time is too long. In that case we need do the
- * 64 bits math carefully
- */
- do_div(max, mult);
- if (cycle_delta > max) {
- num = div64_u64(cycle_delta, max);
- nsec = (((u64) max * mult) >> shift) * num;
- cycle_delta -= num * max;
- }
- nsec += ((u64) cycle_delta * mult) >> shift;
+ u64 nsec, cyc_delta;

+ cyc_delta = clocksource_delta(cycle_now, tk->tkr_mono.cycle_last,
+ tk->tkr_mono.mask);
+ nsec = mul_u64_u32_shr(cyc_delta, clock->mult, clock->shift);
ts_delta = ns_to_timespec64(nsec);
sleeptime_injected = true;
} else if (timespec64_compare(&ts_new, &timekeeping_suspend_time) > 0) {