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Subject[PATCH] Timer bug fix ported to 2.4.20
I recently upgraded from 2.2.19 to 2.4.20 and noted that the via timer
bugfix has disappeared.

I'm not sure if this is a VIA problem, because it happens on my PIII
i440BX-based board, Gigabyte GA-6BXE, which does not seem to have any
chips made by VIA. (82443BX, 32371EB PIIX4, ITE 8671 SuperIO)

However, whenever i start X, the system clock slows down significantly
(it takes about 10 real seconds for 1 system second to elapse).

The only patch I could find for this was the one by Neale Banks:
http://www.uwsg.iu.edu/hypermail/linux/kernel/0204.1/0005.html

I ported this to 2.4.20 and it works (at least for me..)
It can still be disabled with "timer=no-via686a" (from the original patch)

Any comments? (I'm not subscribed to linux-kernel)

Here is some dmesg output generated by the patch:

timer.c: VIA bug check triggered. Value read 62758 [0xf526], re-read 62758 [0xf526]
timer.c VIA bug really present. <4>Resetting PIT timer.
Resetting PIT timer.
Resetting PIT timer.
timer.c: VIA bug check triggered. Value read 62762 [0xf52a], re-read 62762 [0xf52a]
timer.c VIA bug really present. <4>Resetting PIT timer.
Resetting PIT timer.
Resetting PIT timer.
timer.c: VIA bug check triggered. Value read 62756 [0xf524], re-read 62756 [0xf524]
timer.c VIA bug really present. <4>Resetting PIT timer.
Resetting PIT timer.
Resetting PIT timer.
Resetting PIT timer.
timer.c: VIA bug check triggered. Value read 62760 [0xf528], re-read 62760 [0xf528]
timer.c VIA bug really present. <4>Resetting PIT timer.
Resetting PIT timer.
Resetting PIT timer.


Cheers,
Robert


--- linux-2.4.20/arch/i386/kernel/time.c.orig 2003-01-15 11:33:04.000000000 +0100
+++ linux-2.4.20/arch/i386/kernel/time.c 2003-01-16 16:48:32.000000000 +0100
@@ -84,6 +84,8 @@

spinlock_t rtc_lock = SPIN_LOCK_UNLOCKED;

+static int via686a_hacks = 1; /* default to enabled */
+
static inline unsigned long do_fast_gettimeoffset(void)
{
register unsigned long eax, edx;
@@ -113,6 +115,54 @@
return delay_at_last_interrupt + edx;
}

+/*
+ * VIA hardware bug workaround with check if it is really needed and
+ * a printk that could tell us what's exactly happening on machines which
+ * trigger the check, but are not VIA-based.
+ *
+ * Must be called with the i8253_spinlock held.
+ */
+
+static void via_reset_and_whine(int *count)
+{
+ static unsigned long last_whine = 0;
+ unsigned long new_whine;
+ int count2;
+
+ new_whine = last_whine;
+
+ outb_p(0x00, 0x43); /* Re-read the timer */
+ count2 = inb_p(0x40);
+ count2 |= inb(0x40) << 8;
+
+ if (time_after(jiffies, last_whine)) {
+ printk(KERN_WARNING "timer.c: VIA bug check triggered. "
+ "Value read %d [%#x], re-read %d [%#x]\n",
+ *count, *count, count2, count2);
+ new_whine = jiffies + HZ;
+ }
+
+ *count = count2;
+
+ if (count2 > LATCH) { /* Still bad */
+ if (time_after(jiffies, last_whine)) {
+ printk(KERN_WARNING "timer.c VIA bug really present. ");
+ new_whine = jiffies + HZ;
+ }
+ if (via686a_hacks) {
+ printk(KERN_WARNING "Resetting PIT timer.\n");
+ outb_p(0x34, 0x43);
+ outb_p(LATCH & 0xff, 0x40);
+ outb(LATCH >> 8, 0x40);
+ } else {
+ printk(KERN_WARNING "But VIA hacks disabled.\n");
+ }
+ *count = LATCH - 1;
+ }
+
+ last_whine = new_whine;
+}
+
#define TICK_SIZE tick

spinlock_t i8253_lock = SPIN_LOCK_UNLOCKED;
@@ -184,10 +234,7 @@

/* VIA686a test code... reset the latch if count > max + 1 */
if (count > LATCH) {
- outb_p(0x34, 0x43);
- outb_p(LATCH & 0xff, 0x40);
- outb(LATCH >> 8, 0x40);
- count = LATCH - 1;
+ via_reset_and_whine(&count);
}

spin_unlock(&i8253_lock);
@@ -504,6 +551,8 @@

count = inb_p(0x40); /* read the latched count */
count |= inb(0x40) << 8;
+ if (count > LATCH)
+ via_reset_and_whine(&count);
spin_unlock(&i8253_lock);

count = ((LATCH-1) - count) * TICK_SIZE;
@@ -717,3 +766,25 @@
setup_irq(0, &irq0);
#endif
}
+
+static int __init timer_setup(char *str)
+{
+ int invert;
+
+ while ((str != NULL) && (*str != '\0')) {
+ invert = (strncmp(str, "no-", 3) == 0);
+ if (invert)
+ str += 3;
+ if (strncmp(str, "via686a", 7) == 0) {
+ via686a_hacks = !invert;
+ if (invert)
+ printk(KERN_INFO "timer: VIA686a workaround disabled.\n");
+ }
+ str = strchr(str, ',');
+ if (str != NULL)
+ str += strspn(str, ", \t");
+ }
+ return 1;
+}
+
+__setup("timer=", timer_setup);
-
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