diff mbox series

[3/7] timecounter: allow for non-power of two overflow

Message ID 20211104133204.19757-4-martin.kaistra@linutronix.de (mailing list archive)
State Superseded
Headers show
Series Add PTP support for BCM53128 switch | expand

Checks

Context Check Description
netdev/fixes_present success Fixes tag not required for -next series
netdev/subject_prefix success Link
netdev/cover_letter success Series has a cover letter
netdev/patch_count success Link
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 482 this patch: 482
netdev/cc_maintainers success CCed 4 of 4 maintainers
netdev/build_clang success Errors and warnings before: 158 this patch: 158
netdev/module_param success Was 0 now: 0
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 523 this patch: 523
netdev/checkpatch warning WARNING: line length of 82 exceeds 80 columns
netdev/kdoc success Errors and warnings before: 1 this patch: 1
netdev/source_inline success Was 0 now: 0
netdev/tree_selection success Guessing tree name failed - patch did not apply

Commit Message

Martin Kaistra Nov. 4, 2021, 1:31 p.m. UTC 
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 mbox series

Patch

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);