Guard against the i8254 timer being uninitialzed if DELAY() is

called early for console i/o.  The timer is usually in BIOS mode
if it isn't explicitly initialized.  Then it counts twice as fast
and has a max count of 65535 instead of 11932.  The larger count
tended to cause infinite loops for delays of > 20 us.  Such delays
are rare.  For syscons and kbdio, DELAY() is only called early
enough to matter for ddb input after booting with -d, and the delay
is too small to matter (and too small to be correct) except in the
PC98 case.  For pcvt, DELAY() is not used for small delays (pcvt
uses its own broken routine instead of the standard broken one),
but some versions call DELAY() with a large arg when they unnecessarily
initialize the keyboard for doing console output.  The problem is
more serious for pcvt because there is always some early console
output.

Guard against the i8254 timer being partially or incorrectly
initialized.  This would have prevented the endless loop.

Should be in 2.2.

1 files changed, 22 insertions, 5 deletions

diff --git a/sys/amd64/isa/clock.c b/sys/amd64/isa/clock.c
index 9319e4c..faa38fd 100644
--- a/sys/amd64/isa/clock.c
+++ b/sys/amd64/isa/clock.c
@@ -146,6 +146,7 @@ static	void	(*timer_func) __P((struct clockframe *frame)) = hardclock;
 #if defined(I586_CPU) || defined(I686_CPU)
 static	void	set_i586_ctr_freq(u_int i586_freq, u_int i8254_freq);
 #endif
+static	void	set_timer_freq(u_int freq, int intr_freq);
 
 static void
 clkintr(struct clockframe frame)
@@ -361,7 +362,7 @@ getit(void)
 void
 DELAY(int n)
 {
-	int prev_tick, tick, ticks_left, sec, usec;
+	int delta, prev_tick, tick, ticks_left, sec, usec;
 
 #ifdef DELAYDEBUG
 	int getit_calls = 1;
@@ -378,6 +379,13 @@ DELAY(int n)
 		printf("DELAY(%d)...", n);
 #endif
 	/*
+	 * Guard against the timer being uninitialized if we are called
+	 * early for console i/o.
+	 */
+	if (timer0_max_count == 0)
+		set_timer_freq(timer_freq, hz);
+
+	/*
 	 * Read the counter first, so that the rest of the setup overhead is
 	 * counted.  Guess the initial overhead is 20 usec (on most systems it
 	 * takes about 1.5 usec for each of the i/o's in getit().  The loop
@@ -404,11 +412,20 @@ DELAY(int n)
 #ifdef DELAYDEBUG
 		++getit_calls;
 #endif
-		if (tick > prev_tick)
-			ticks_left -= prev_tick - (tick - timer0_max_count);
-		else
-			ticks_left -= prev_tick - tick;
+		delta = prev_tick - tick;
 		prev_tick = tick;
+		if (delta < 0) {
+			delta += timer0_max_count;
+			/*
+			 * Guard against timer0_max_count being wrong.
+			 * This shouldn't happen in normal operation,
+			 * but it may happen if set_timer_freq() is
+			 * traced.
+			 */
+			if (delta < 0)
+				delta = 0;
+		}
+		ticks_left -= delta;
 	}
 #ifdef DELAYDEBUG
 	if (state == 1)