1. Fix a comment. Locking _is_ needed (but not done).

2. Update a comment.  We now restore much more than RTC updates and
   interrupts.
3. Order change.  Stop interrupts by writing to RTC_STATUSB,
   restore rate bits for the interrupts by writing to RTC_STATUSA,
   then enable interrupts again.
   This seems to be done perfectly backwards in startrtclock().
   Otherwise, the idea for this change was obtained from
   startrtclock().
4. Don't stop the clock (RTCB_HALT).  We only program some control bits
   and don't want to stop the clock.
5. (Not really related.)  Add caveats to the comment about timer_restore().
   The update is non-atomic since locking is not done.

On locking:
6. rtcin() and writertc() are locked() adequately by splhigh() in RELENG_4,
   but this locking is null in -current.
7. Doing things in the correct order in (3) combined with (6) is probably
   enough locking for rtcrestore() in RELENG_4.  In -current, the
   writertc()'s race with rtcintr() unless the BIOS disables RTC interrupts.

Submitted by:	bde (including commit message)
MFC after:	1 week

1 files changed, 8 insertions, 12 deletions

diff --git a/sys/amd64/isa/clock.c b/sys/amd64/isa/clock.c
index ff37d5d..93d486c 100644
--- a/sys/amd64/isa/clock.c
+++ b/sys/amd64/isa/clock.c
@@ -692,14 +692,6 @@ set_timer_freq(u_int freq, int intr_freq)
 	mtx_unlock_spin(&clock_lock);
 }
 
-/*
- * i8254_restore is called from apm_default_resume() to reload
- * the countdown register.
- * this should not be necessary but there are broken laptops that
- * do not restore the countdown register on resume.
- * when it happnes, it messes up the hardclock interval and system clock,
- * which leads to the infamous "calcru: negative time" problem.
- */
 static void
 i8254_restore(void)
 {
@@ -715,15 +707,19 @@ static void
 rtc_restore(void)
 {
 
-	/* Reenable RTC updates and interrupts. */
-	/* XXX locking is needed for RTC access? */
+	/* Restore all of the RTC's "status" (actually, control) registers. */
+	/* XXX locking is needed for RTC access. */
+	writertc(RTC_STATUSB, RTCSB_24HR);
 	writertc(RTC_STATUSA, rtc_statusa);
-	writertc(RTC_STATUSB, RTCSB_HALT | RTCSB_24HR);
 	writertc(RTC_STATUSB, rtc_statusb);
 }
 
 /*
- * Restore all the timers atomically.
+ * Restore all the timers non-atomically (XXX: should be atomically).
+ *
+ * This function is called from pmtimer_resume() to restore all the timers.
+ * This should not be necessary, but there are broken laptops that do not
+ * restore all the timers on resume.
  */
 void
 timer_restore(void)