[PATCH] i386: fix hpet for systems that don't support legacy replacement

Currently the i386 HPET code assumes the entire HPET implementation from
the spec is present.  This breaks on boxes that do not implement the
optional legacy timer replacement functionality portion of the spec.

This patch, which is very similar to my x86-64 patch for the same issue,
fixes the problem allowing i386 systems that cannot use the HPET for the
timer interrupt and RTC to still use the HPET as a time source.  I've
tested this patch on a system systems without HPET, with HPET but without
legacy timer replacement, as well as HPET with legacy timer replacement.

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 8 insertions, 5 deletions

diff --git a/arch/i386/kernel/timers/timer_hpet.c b/arch/i386/kernel/timers/timer_hpet.c
index 713134e71844..f778f471a09a 100644
--- a/arch/i386/kernel/timers/timer_hpet.c
+++ b/arch/i386/kernel/timers/timer_hpet.c
@@ -79,7 +79,7 @@ static unsigned long get_offset_hpet(void)
 
         eax = hpet_readl(HPET_COUNTER);
         eax -= hpet_last;       /* hpet delta */
-
+        eax = min(hpet_tick, eax);
         /*
          * Time offset = (hpet delta) * ( usecs per HPET clock )
          *             = (hpet delta) * ( usecs per tick / HPET clocks per tick)
@@ -105,9 +105,12 @@ static void mark_offset_hpet(void)
         last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
         rdtsc(last_tsc_low, last_tsc_high);
 
-        offset = hpet_readl(HPET_T0_CMP) - hpet_tick;
-        if (unlikely(((offset - hpet_last) > hpet_tick) && (hpet_last != 0))) {
-                int lost_ticks = (offset - hpet_last) / hpet_tick;
+        if (hpet_use_timer)
+                offset = hpet_readl(HPET_T0_CMP) - hpet_tick;
+        else
+                offset = hpet_readl(HPET_COUNTER);
+        if (unlikely(((offset - hpet_last) >= (2*hpet_tick)) && (hpet_last != 0))) {
+                int lost_ticks = ((offset - hpet_last) / hpet_tick) - 1;
                 jiffies_64 += lost_ticks;
         }
         hpet_last = offset;
diff --git a/arch/i386/kernel/timers/timer_tsc.c b/arch/i386/kernel/timers/timer_tsc.c
index a685994e5c8e..7926d967be00 100644
--- a/arch/i386/kernel/timers/timer_tsc.c
+++ b/arch/i386/kernel/timers/timer_tsc.c
@@ -477,7 +477,7 @@ static int __init init_tsc(char* override)
         if (cpu_has_tsc) {
                 unsigned long tsc_quotient;
 #ifdef CONFIG_HPET_TIMER
-                if (is_hpet_enabled()){
+                if (is_hpet_enabled() && hpet_use_timer) {
                         unsigned long result, remain;
                         printk("Using TSC for gettimeofday\n");
                         tsc_quotient = calibrate_tsc_hpet(NULL);