Merge tag 'timers-core-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull timers and timekeeping updates from Thomas Gleixner:
 "Core:

   - Robustness improvements for the NOHZ tick management

   - Fixes and consolidation of the NTP/RTC synchronization code

   - Small fixes and improvements in various places

   - A set of function documentation udpates and fixes

   Drivers:

   - Cleanups and improvements in various clocksoure/event drivers

   - Removal of the EZChip NPS clocksource driver as the platfrom
     support was removed from ARC

   - The usual set of new device tree binding and json conversions

   - The RTC driver which have been acked by the RTC maintainer:

       * fix a long standing bug in the MC146818 library code which can
         cause reading garbage during the RTC internal update.

       * changes related to the NTP/RTC consolidation work"

* tag 'timers-core-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (46 commits)
  ntp: Fix prototype in the !CONFIG_GENERIC_CMOS_UPDATE case
  tick/sched: Make jiffies update quick check more robust
  ntp: Consolidate the RTC update implementation
  ntp: Make the RTC sync offset less obscure
  ntp, rtc: Move rtc_set_ntp_time() to ntp code
  ntp: Make the RTC synchronization more reliable
  rtc: core: Make the sync offset default more realistic
  rtc: cmos: Make rtc_cmos sync offset correct
  rtc: mc146818: Reduce spinlock section in mc146818_set_time()
  rtc: mc146818: Prevent reading garbage
  clocksource/drivers/sh_cmt: Fix potential deadlock when calling runtime PM
  clocksource/drivers/arm_arch_timer: Correct fault programming of CNTKCTL_EL1.EVNTI
  clocksource/drivers/arm_arch_timer: Use stable count reader in erratum sne
  clocksource/drivers/dw_apb_timer_of: Add error handling if no clock available
  clocksource/drivers/riscv: Make RISCV_TIMER depends on RISCV_SBI
  clocksource/drivers/ingenic: Fix section mismatch
  clocksource/drivers/cadence_ttc: Fix memory leak in ttc_setup_clockevent()
  dt-bindings: timer: renesas: tmu: Convert to json-schema
  dt-bindings: timer: renesas: tmu: Document r8a774e1 bindings
  clocksource/drivers/orion: Add missing clk_disable_unprepare() on error path
  ...

1 files changed, 29 insertions, 40 deletions

diff --git a/include/linux/rtc.h b/include/linux/rtc.h
index 22d1575e4991..b829382de6c3 100644
--- a/include/linux/rtc.h
+++ b/include/linux/rtc.h
@@ -110,13 +110,36 @@ struct rtc_device {
 	/* Some hardware can't support UIE mode */
 	int uie_unsupported;
 
-	/* Number of nsec it takes to set the RTC clock. This influences when
-	 * the set ops are called. An offset:
-	 *   - of 0.5 s will call RTC set for wall clock time 10.0 s at 9.5 s
-	 *   - of 1.5 s will call RTC set for wall clock time 10.0 s at 8.5 s
-	 *   - of -0.5 s will call RTC set for wall clock time 10.0 s at 10.5 s
+	/*
+	 * This offset specifies the update timing of the RTC.
+	 *
+	 * tsched     t1 write(t2.tv_sec - 1sec))  t2 RTC increments seconds
+	 *
+	 * The offset defines how tsched is computed so that the write to
+	 * the RTC (t2.tv_sec - 1sec) is correct versus the time required
+	 * for the transport of the write and the time which the RTC needs
+	 * to increment seconds the first time after the write (t2).
+	 *
+	 * For direct accessible RTCs tsched ~= t1 because the write time
+	 * is negligible. For RTCs behind slow busses the transport time is
+	 * significant and has to be taken into account.
+	 *
+	 * The time between the write (t1) and the first increment after
+	 * the write (t2) is RTC specific. For a MC146818 RTC it's 500ms,
+	 * for many others it's exactly 1 second. Consult the datasheet.
+	 *
+	 * The value of this offset is also used to calculate the to be
+	 * written value (t2.tv_sec - 1sec) at tsched.
+	 *
+	 * The default value for this is NSEC_PER_SEC + 10 msec default
+	 * transport time. The offset can be adjusted by drivers so the
+	 * calculation for the to be written value at tsched becomes
+	 * correct:
+	 *
+	 *	newval = tsched + set_offset_nsec - NSEC_PER_SEC
+	 * and  (tsched + set_offset_nsec) % NSEC_PER_SEC == 0
 	 */
-	long set_offset_nsec;
+	unsigned long set_offset_nsec;
 
 	bool registered;
 
@@ -165,7 +188,6 @@ int __rtc_register_device(struct module *owner, struct rtc_device *rtc);
 
 extern int rtc_read_time(struct rtc_device *rtc, struct rtc_time *tm);
 extern int rtc_set_time(struct rtc_device *rtc, struct rtc_time *tm);
-extern int rtc_set_ntp_time(struct timespec64 now, unsigned long *target_nsec);
 int __rtc_read_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm);
 extern int rtc_read_alarm(struct rtc_device *rtc,
 			struct rtc_wkalrm *alrm);
@@ -205,39 +227,6 @@ static inline bool is_leap_year(unsigned int year)
 	return (!(year % 4) && (year % 100)) || !(year % 400);
 }
 
-/* Determine if we can call to driver to set the time. Drivers can only be
- * called to set a second aligned time value, and the field set_offset_nsec
- * specifies how far away from the second aligned time to call the driver.
- *
- * This also computes 'to_set' which is the time we are trying to set, and has
- * a zero in tv_nsecs, such that:
- *    to_set - set_delay_nsec == now +/- FUZZ
- *
- */
-static inline bool rtc_tv_nsec_ok(s64 set_offset_nsec,
-				  struct timespec64 *to_set,
-				  const struct timespec64 *now)
-{
-	/* Allowed error in tv_nsec, arbitarily set to 5 jiffies in ns. */
-	const unsigned long TIME_SET_NSEC_FUZZ = TICK_NSEC * 5;
-	struct timespec64 delay = {.tv_sec = 0,
-				   .tv_nsec = set_offset_nsec};
-
-	*to_set = timespec64_add(*now, delay);
-
-	if (to_set->tv_nsec < TIME_SET_NSEC_FUZZ) {
-		to_set->tv_nsec = 0;
-		return true;
-	}
-
-	if (to_set->tv_nsec > NSEC_PER_SEC - TIME_SET_NSEC_FUZZ) {
-		to_set->tv_sec++;
-		to_set->tv_nsec = 0;
-		return true;
-	}
-	return false;
-}
-
 #define rtc_register_device(device) \
 	__rtc_register_device(THIS_MODULE, device)