1 files changed, 31 insertions, 6 deletions

diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c
index 7a9b18224182..7700e6cd2bd9 100644
--- a/arch/x86_64/kernel/time.c
+++ b/arch/x86_64/kernel/time.c
@@ -1148,23 +1148,25 @@ int hpet_rtc_timer_init(void)
                 hpet_rtc_int_freq = DEFAULT_RTC_INT_FREQ;
 
         local_irq_save(flags);
+
         cnt = hpet_readl(HPET_COUNTER);
         cnt += ((hpet_tick*HZ)/hpet_rtc_int_freq);
         hpet_writel(cnt, HPET_T1_CMP);
         hpet_t1_cmp = cnt;
-        local_irq_restore(flags);
 
         cfg = hpet_readl(HPET_T1_CFG);
         cfg &= ~HPET_TN_PERIODIC;
         cfg |= HPET_TN_ENABLE | HPET_TN_32BIT;
         hpet_writel(cfg, HPET_T1_CFG);
 
+        local_irq_restore(flags);
+
         return 1;
 }
 
 static void hpet_rtc_timer_reinit(void)
 {
-        unsigned int cfg, cnt;
+        unsigned int cfg, cnt, ticks_per_int, lost_ints;
 
         if (unlikely(!(PIE_on | AIE_on | UIE_on))) {
                 cfg = hpet_readl(HPET_T1_CFG);
@@ -1179,10 +1181,33 @@ static void hpet_rtc_timer_reinit(void)
                 hpet_rtc_int_freq = DEFAULT_RTC_INT_FREQ;
 
         /* It is more accurate to use the comparator value than current count.*/
-        cnt = hpet_t1_cmp;
-        cnt += hpet_tick*HZ/hpet_rtc_int_freq;
-        hpet_writel(cnt, HPET_T1_CMP);
-        hpet_t1_cmp = cnt;
+        ticks_per_int = hpet_tick * HZ / hpet_rtc_int_freq;
+        hpet_t1_cmp += ticks_per_int;
+        hpet_writel(hpet_t1_cmp, HPET_T1_CMP);
+
+        /*
+         * If the interrupt handler was delayed too long, the write above tries
+         * to schedule the next interrupt in the past and the hardware would
+         * not interrupt until the counter had wrapped around.
+         * So we have to check that the comparator wasn't set to a past time.
+         */
+        cnt = hpet_readl(HPET_COUNTER);
+        if (unlikely((int)(cnt - hpet_t1_cmp) > 0)) {
+                lost_ints = (cnt - hpet_t1_cmp) / ticks_per_int + 1;
+                /* Make sure that, even with the time needed to execute
+                 * this code, the next scheduled interrupt has been moved
+                 * back to the future: */
+                lost_ints++;
+
+                hpet_t1_cmp += lost_ints * ticks_per_int;
+                hpet_writel(hpet_t1_cmp, HPET_T1_CMP);
+
+                if (PIE_on)
+                        PIE_count += lost_ints;
+
+                printk(KERN_WARNING "rtc: lost some interrupts at %ldHz.\n",
+                       hpet_rtc_int_freq);
+        }
 }
 
 /*