[PATCH 3/7] timecounter: allow for non-power of two overflow
From: Martin Kaistra <hidden>
Date: 2021-11-04 13:33:06
Also in:
lkml
Subsystem:
the rest, timekeeping, clocksource core, ntp, alarmtimer · Maintainers:
Linus Torvalds, John Stultz, Thomas Gleixner
Some hardware counters which are used as clocks have an overflow point which is not a power of two. In order to be able to use the cycle counter infrastructure with such hardware, add support for more generic overflow logic. Signed-off-by: Martin Kaistra <redacted> --- include/linux/timecounter.h | 3 +++ kernel/time/timecounter.c | 3 +++ 2 files changed, 6 insertions(+)
diff --git a/include/linux/timecounter.h b/include/linux/timecounter.h
index c6540ceea143..c71196a742b3 100644
--- a/include/linux/timecounter.h
+++ b/include/linux/timecounter.h@@ -26,12 +26,15 @@ * see CYCLECOUNTER_MASK() helper macro * @mult: cycle to nanosecond multiplier * @shift: cycle to nanosecond divisor (power of two) + * @overflow_point: non-power of two overflow point (optional), + * smaller than mask */ struct cyclecounter { u64 (*read)(const struct cyclecounter *cc); u64 mask; u32 mult; u32 shift; + u64 overflow_point; }; /**
diff --git a/kernel/time/timecounter.c b/kernel/time/timecounter.c
index e6285288d765..afd2910a9724 100644
--- a/kernel/time/timecounter.c
+++ b/kernel/time/timecounter.c@@ -39,6 +39,9 @@ static u64 timecounter_read_delta(struct timecounter *tc) /* calculate the delta since the last timecounter_read_delta(): */ cycle_delta = (cycle_now - tc->cycle_last) & tc->cc->mask; + if (tc->cc->overflow_point && (cycle_now - tc->cycle_last) > tc->cc->mask) + cycle_delta -= tc->cc->mask - tc->cc->overflow_point; + /* convert to nanoseconds: */ ns_offset = cyclecounter_cyc2ns(tc->cc, cycle_delta, tc->mask, &tc->frac);
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2.20.1