Merge tag 'timers-core-2022-01-13' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull timer updates from Thomas Gleixner:
 "Updates for the time(r) subsystem:

  Core:

   - Make the clocksource watchdog more robust by better validation
     checks of the measurement.

  Drivers:

   - New drivers for MStar and SSD20xd SOCs

   - The usual cleanups and improvements all over the place"

* tag 'timers-core-2022-01-13' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  dt-bindings: timer: Add Mstar MSC313e timer devicetree bindings documentation
  clocksource/drivers/msc313e: Add support for ssd20xd-based platforms
  clocksource/drivers: Add MStar MSC313e timer support
  clocksource/drivers/pistachio: Fix -Wunused-but-set-variable warning
  clocksource/drivers/timer-imx-sysctr: Set cpumask to cpu_possible_mask
  clocksource/drivers/imx-sysctr: Mark two variable with __ro_after_init
  clocksource/drivers/renesas,ostm: Make RENESAS_OSTM symbol visible
  clocksource/drivers/renesas-ostm: Add RZ/G2L OSTM support
  dt-bindings: timer: renesas: ostm: Document Renesas RZ/G2L OSTM
  clocksource/drivers/exynos_mct: Fix silly typo resulting in checkpatch warning
  clocksource: Reduce the default clocksource_watchdog() retries to 2
  clocksource: Avoid accidental unstable marking of clocksources
  dt-bindings: timer: tpm-timer: Add imx8ulp compatible string
  reset: Add of_reset_control_get_optional_exclusive()
  clocksource/drivers/exynos_mct: Refactor resources allocation
  dt-bindings: timer: remove rockchip,rk3066-timer compatible string from rockchip,rk-timer.yaml
  dt-bindings: timer: cadence_ttc: Add power-domains

kernel/time/clocksource.c

@@ -107,7 +107,7 @@ static u64 suspend_start;
  * This delay could be due to SMIs, NMIs, or to VCPU preemptions.  Used as
  * a lower bound for cs->uncertainty_margin values when registering clocks.
  */
-#define WATCHDOG_MAX_SKEW (50 * NSEC_PER_USEC)
+#define WATCHDOG_MAX_SKEW (100 * NSEC_PER_USEC)
 
 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
 static void clocksource_watchdog_work(struct work_struct *work);
@@ -199,23 +199,30 @@ void clocksource_mark_unstable(struct clocksource *cs)
 	spin_unlock_irqrestore(&watchdog_lock, flags);
 }
 
-ulong max_cswd_read_retries = 3;
+ulong max_cswd_read_retries = 2;
 module_param(max_cswd_read_retries, ulong, 0644);
 EXPORT_SYMBOL_GPL(max_cswd_read_retries);
 static int verify_n_cpus = 8;
 module_param(verify_n_cpus, int, 0644);
 
-static bool cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow)
+enum wd_read_status {
+	WD_READ_SUCCESS,
+	WD_READ_UNSTABLE,
+	WD_READ_SKIP
+};
+
+static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow)
 {
 	unsigned int nretries;
-	u64 wd_end, wd_delta;
-	int64_t wd_delay;
+	u64 wd_end, wd_end2, wd_delta;
+	int64_t wd_delay, wd_seq_delay;
 
 	for (nretries = 0; nretries <= max_cswd_read_retries; nretries++) {
 		local_irq_disable();
 		*wdnow = watchdog->read(watchdog);
 		*csnow = cs->read(cs);
 		wd_end = watchdog->read(watchdog);
+		wd_end2 = watchdog->read(watchdog);
 		local_irq_enable();
 
 		wd_delta = clocksource_delta(wd_end, *wdnow, watchdog->mask);
@@ -226,13 +233,34 @@ static bool cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow)
 				pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before success\n",
 					smp_processor_id(), watchdog->name, nretries);
 			}
-			return true;
+			return WD_READ_SUCCESS;
 		}
+
+		/*
+		 * Now compute delay in consecutive watchdog read to see if
+		 * there is too much external interferences that cause
+		 * significant delay in reading both clocksource and watchdog.
+		 *
+		 * If consecutive WD read-back delay > WATCHDOG_MAX_SKEW/2,
+		 * report system busy, reinit the watchdog and skip the current
+		 * watchdog test.
+		 */
+		wd_delta = clocksource_delta(wd_end2, wd_end, watchdog->mask);
+		wd_seq_delay = clocksource_cyc2ns(wd_delta, watchdog->mult, watchdog->shift);
+		if (wd_seq_delay > WATCHDOG_MAX_SKEW/2)
+			goto skip_test;
 	}
 
 	pr_warn("timekeeping watchdog on CPU%d: %s read-back delay of %lldns, attempt %d, marking unstable\n",
 		smp_processor_id(), watchdog->name, wd_delay, nretries);
-	return false;
+	return WD_READ_UNSTABLE;
+
+skip_test:
+	pr_info("timekeeping watchdog on CPU%d: %s wd-wd read-back delay of %lldns\n",
+		smp_processor_id(), watchdog->name, wd_seq_delay);
+	pr_info("wd-%s-wd read-back delay of %lldns, clock-skew test skipped!\n",
+		cs->name, wd_delay);
+	return WD_READ_SKIP;
 }
 
 static u64 csnow_mid;
@@ -356,6 +384,7 @@ static void clocksource_watchdog(struct timer_list *unused)
 	int next_cpu, reset_pending;
 	int64_t wd_nsec, cs_nsec;
 	struct clocksource *cs;
+	enum wd_read_status read_ret;
 	u32 md;
 
 	spin_lock(&watchdog_lock);
@@ -373,9 +402,12 @@ static void clocksource_watchdog(struct timer_list *unused)
 			continue;
 		}
 
-		if (!cs_watchdog_read(cs, &csnow, &wdnow)) {
-			/* Clock readout unreliable, so give it up. */
-			__clocksource_unstable(cs);
+		read_ret = cs_watchdog_read(cs, &csnow, &wdnow);
+
+		if (read_ret != WD_READ_SUCCESS) {
+			if (read_ret == WD_READ_UNSTABLE)
+				/* Clock readout unreliable, so give it up. */
+				__clocksource_unstable(cs);
 			continue;
 		}