From 7ab95d0bab5a696c9cc7f2ade873106fb53a772f Mon Sep 17 00:00:00 2001
From: Poul-Henning Kamp <phk@FreeBSD.org>
Date: Mon, 16 Mar 1998 10:06:58 +0000
Subject: Be less draconian about the TSC if APM is configured, use it for
 timecounting if APM-BIOS isn't found. Be just as draconian about SMP as
 always, but explain it better.

---
 sys/i386/isa/clock.c | 39 +++++++++++++++++++++++++++++++--------
 1 file changed, 31 insertions(+), 8 deletions(-)

(limited to 'sys/i386/isa/clock.c')

diff --git a/sys/i386/isa/clock.c b/sys/i386/isa/clock.c
index 607b34029f7d..65881655b0a3 100644
--- a/sys/i386/isa/clock.c
+++ b/sys/i386/isa/clock.c
@@ -34,7 +34,7 @@
  * SUCH DAMAGE.
  *
  *	from: @(#)clock.c	7.2 (Berkeley) 5/12/91
- *	$Id: clock.c,v 1.115 1998/03/05 21:45:48 tegge Exp $
+ *	$Id: clock.c,v 1.116 1998/03/14 03:11:50 tegge Exp $
  */
 
 /*
@@ -69,6 +69,10 @@
 #include <machine/ipl.h>
 #include <machine/limits.h>
 #include <machine/md_var.h>
+#if NAPM > 0
+#include <machine/apm_bios.h>
+#include <i386/apm/apm_setup.h>
+#endif
 #ifdef APIC_IO
 #include <machine/segments.h>
 #endif
@@ -689,13 +693,6 @@ startrtclock()
 	else
 		tsc_present = 0;
 
-#ifdef SMP
-	tsc_present = 0;
-#endif
-#if NAPM > 0
-	tsc_present = 0;
-#endif
-	
 	writertc(RTC_STATUSA, rtc_statusa);
 	writertc(RTC_STATUSB, RTCSB_24HR);
 
@@ -758,10 +755,36 @@ startrtclock()
 			printf("TSC clock: %u Hz (Method B)\n", tsc_freq);
 #endif
 	}
+
+#if !defined(SMP)
+	/*
+	 * We can not use the TSC in SMP mode, until we figure out a
+	 * cheap (impossible), reliable and precise (yeah right!)  way
+	 * to synchronize the TSCs of all the CPUs.
+	 * Curse Intel for leaving the counter out of the I/O APIC.
+	 */
+
+#if NAPM > 0
+	/*
+	 * We can not use the TSC if we found an APM bios.  Too many
+	 * of them lie about their ability&intention to fiddle the CPU
+	 * clock for us to rely on this.  Precise timekeeping on an
+	 * APM'ed machine is at best a fools pursuit anyway, since 
+	 * any and all of the time spent in various SMM code can't 
+	 * be reliably accounted for.  Reading the RTC is your only
+	 * source of reliable time info.  The i8254 looses too of course
+	 * but we need to have some kind of time...
+	 */
+	if (apm_version != APMINI_CANTFIND)
+		return;
+#endif /* NAPM > 0 */
+
 	if (tsc_present && tsc_freq != 0) {
 		tsc_timecounter[0].frequency = tsc_freq;
 		init_timecounter(tsc_timecounter);
 	}
+
+#endif /* !defined(SMP) */
 }
 
 /*
-- 
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