From 27dca831a651289cb6506fb213739cfda3dce49a Mon Sep 17 00:00:00 2001
From: Andriy Gapon <avg@FreeBSD.org>
Date: Mon, 21 May 2018 20:23:04 +0000
Subject: [PATCH] stop and restart kernel event timers in the suspend / resume
 cycle

I have a system that is very unstable after resuming from suspend-to-RAM
but only if HPET is used as the event timer.  The theory is that SMM
code / firmware could be enabling HPET for its own uses and unexpected
interrupts cause a trouble for it.  Originally I wanted to solve the
problem in hpet_suspend() method, but that was insufficient as the event
timer could get reprogrammed again.

So, it's better, for my case and in general, to stop the event timer(s)
before entering the hardware suspend.

MFC after:	4 weeks
Differential Revision: https://reviews.freebsd.org/D15413
---
 sys/dev/acpica/acpi.c       |  3 +++
 sys/kern/kern_clocksource.c | 16 ++++++++++++++++
 sys/sys/systm.h             |  2 ++
 3 files changed, 21 insertions(+)

diff --git a/sys/dev/acpica/acpi.c b/sys/dev/acpica/acpi.c
index 33f88b2839f..aec4e278053 100644
--- a/sys/dev/acpica/acpi.c
+++ b/sys/dev/acpica/acpi.c
@@ -2958,6 +2958,7 @@ acpi_EnterSleepState(struct acpi_softc *sc, int state)
     if (sc->acpi_sleep_delay > 0)
 	DELAY(sc->acpi_sleep_delay * 1000000);
 
+    suspendclock();
     intr = intr_disable();
     if (state != ACPI_STATE_S1) {
 	sleep_result = acpi_sleep_machdep(sc, state);
@@ -3028,6 +3029,8 @@ acpi_EnterSleepState(struct acpi_softc *sc, int state)
      * process.  This handles both the error and success cases.
      */
 backout:
+    if (slp_state >= ACPI_SS_SLP_PREP)
+	resumeclock();
     if (slp_state >= ACPI_SS_GPE_SET) {
 	acpi_wake_prep_walk(state);
 	sc->acpi_sstate = ACPI_STATE_S0;
diff --git a/sys/kern/kern_clocksource.c b/sys/kern/kern_clocksource.c
index 7b7ca34e609..9676923104e 100644
--- a/sys/kern/kern_clocksource.c
+++ b/sys/kern/kern_clocksource.c
@@ -698,6 +698,22 @@ cpu_initclocks_ap(void)
 	spinlock_exit();
 }
 
+void
+suspendclock(void)
+{
+	ET_LOCK();
+	configtimer(0);
+	ET_UNLOCK();
+}
+
+void
+resumeclock(void)
+{
+	ET_LOCK();
+	configtimer(1);
+	ET_UNLOCK();
+}
+
 /*
  * Switch to profiling clock rates.
  */
diff --git a/sys/sys/systm.h b/sys/sys/systm.h
index 995e06774d6..2bc0efffc80 100644
--- a/sys/sys/systm.h
+++ b/sys/sys/systm.h
@@ -333,6 +333,8 @@ void	startprofclock(struct proc *);
 void	stopprofclock(struct proc *);
 void	cpu_startprofclock(void);
 void	cpu_stopprofclock(void);
+void	suspendclock(void);
+void	resumeclock(void);
 sbintime_t 	cpu_idleclock(void);
 void	cpu_activeclock(void);
 void	cpu_new_callout(int cpu, sbintime_t bt, sbintime_t bt_opt);