Messages in this thread Patch in this message | | | From | Martin Kaistra <> | Subject | [PATCH v2 3/7] timecounter: allow for non-power of two overflow | Date | Tue, 9 Nov 2021 10:50:05 +0100 |
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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 <martin.kaistra@linutronix.de> --- 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); -- 2.20.1
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