fix for a timer latch bug on the cyrix mediagx and gxm cpus.

based on freebsd pr#6630, netbsd pr#8654, openbsd pr#1492 .
does not affect other cpu models (cyrix or not).
asked by markus@ and testing.

2 files changed, 80 insertions, 18 deletions

diff --git a/sys/arch/i386/i386/machdep.c b/sys/arch/i386/i386/machdep.c
index 1c675f34d30..cdc59b4c026 100644
--- a/sys/arch/i386/i386/machdep.c
+++ b/sys/arch/i386/i386/machdep.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: machdep.c,v 1.204 2002/03/30 09:42:28 mickey Exp $	*/
+/*	$OpenBSD: machdep.c,v 1.205 2002/05/16 15:33:05 mickey Exp $	*/
 /*	$NetBSD: machdep.c,v 1.214 1996/11/10 03:16:17 thorpej Exp $	*/
 
 /*-
@@ -1041,7 +1041,6 @@ cyrix6x86_cpu_setup(cpu_device, model, step)
 	int model, step;
 {
 #if defined(I486_CPU) || defined(I586_CPU) || defined(I686_CPU)
-	extern int cpu_feature;
 
 	switch (model) {
 	case -1: /* M1 w/o cpuid */
@@ -1061,10 +1060,6 @@ cyrix6x86_cpu_setup(cpu_device, model, step)
 
 		printf("%s: xchg bug workaround performed\n", cpu_device);
 		break;	/* fallthrough? */
-	case 4:	/* GXm */
-		/* Unset the TSC bit until calibrate_delay() gets fixed. */
-		cpu_feature &= ~CPUID_TSC;
-		break;
 	}
 #endif
 }
diff --git a/sys/arch/i386/isa/clock.c b/sys/arch/i386/isa/clock.c
index 489a9874593..e86cda7777c 100644
--- a/sys/arch/i386/isa/clock.c
+++ b/sys/arch/i386/isa/clock.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: clock.c,v 1.25 2002/03/14 01:26:33 millert Exp $	*/
+/*	$OpenBSD: clock.c,v 1.26 2002/05/16 15:33:10 mickey Exp $	*/
 /*	$NetBSD: clock.c,v 1.39 1996/05/12 23:11:54 mycroft Exp $	*/
 
 /*-
@@ -149,7 +149,7 @@ u_int mc146818_read(void *, u_int);
 void mc146818_write(void *, u_int, u_int);
 
 #if defined(I586_CPU) || defined(I686_CPU)
-int pentium_mhz;
+int pentium_mhz, clock_broken_latch;
 #endif
 
 #define	SECMIN	((unsigned)60)			/* seconds per minute */
@@ -227,6 +227,21 @@ initrtclock()
 	/* Correct rounding will buy us a better precision in timekeeping */
 	outb(IO_TIMER1, TIMER_DIV(hz) % 256);
 	outb(IO_TIMER1, TIMER_DIV(hz) / 256);
+
+#if defined(CPU_I586) || defined(CPU_I686)
+	{
+		extern int cpu_id;
+		switch (cpu_id) {
+		case 0x440:	/* Cyrix MediaGX */
+		case 0x540:	/* Cyrix GXm */
+			clock_broken_latch = 1;
+			break;
+		default:
+			clock_broken_latch = 0;
+			break;
+		}
+	}
+#endif
 }
 
 int
@@ -260,16 +275,68 @@ rtcintr(arg)
 int
 gettick()
 {
-	u_char lo, hi;
-
-	/* Don't want someone screwing with the counter while we're here. */
-	disable_intr();
-	/* Select counter 0 and latch it. */
-	outb(TIMER_MODE, TIMER_SEL0 | TIMER_LATCH);
-	lo = inb(TIMER_CNTR0);
-	hi = inb(TIMER_CNTR0);
-	enable_intr();
-	return ((hi << 8) | lo);
+
+#if defined(I586_CPU) || defined(I686_CPU)
+	if (clock_broken_latch) {
+		int v1, v2, v3;
+		int w1, w2, w3;
+
+		disable_intr();
+
+		v1 = inb(TIMER_CNTR0);
+		v1 |= inb(TIMER_CNTR0) << 8;
+		v2 = inb(TIMER_CNTR0);
+		v2 |= inb(TIMER_CNTR0) << 8;
+		v3 = inb(TIMER_CNTR0);
+		v3 |= inb(TIMER_CNTR0) << 8;
+
+		enable_intr();
+
+		if (v1 >= v2 && v2 >= v3 && v1 - v3 < 0x200)
+			return (v2);
+
+#define _swap_val(a, b) do { \
+	int c = a; \
+	a = b; \
+	b = c; \
+} while (0)
+
+		/* sort v1 v2 v3 */
+		if (v1 < v2)
+			_swap_val(v1, v2);
+		if (v2 < v3)
+			_swap_val(v2, v3);
+		if (v1 < v2)
+			_swap_val(v1, v2);
+
+		/* compute the middle value */
+		if (v1 - v3 < 0x200)
+			return (v2);
+		w1 = v2 - v3;
+		w2 = v3 - v1 + TIMER_DIV(hz);
+		w3 = v1 - v2;
+		if (w1 >= w2) {
+			if (w1 >= w3)
+				return (v1);
+		} else {
+			if (w2 >= w3)
+				return (v2);
+		}
+		return (v3);
+	} else
+#endif
+	{
+		u_char lo, hi;
+
+		disable_intr();
+		/* Select counter 0 and latch it. */
+		outb(TIMER_MODE, TIMER_SEL0 | TIMER_LATCH);
+		lo = inb(TIMER_CNTR0);
+		hi = inb(TIMER_CNTR0);
+
+		enable_intr();
+		return ((hi << 8) | lo);
+	}
 }
 
 /*