1 files changed, 28 insertions, 14 deletions

diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c
index fb8c809b4cd9..66bf6ddeb0c3 100644
--- a/arch/x86_64/kernel/time.c
+++ b/arch/x86_64/kernel/time.c
@@ -64,6 +64,7 @@ static int notsc __initdata = 0;
 unsigned int cpu_khz;                                   /* TSC clocks / usec, not used here */
 static unsigned long hpet_period;                       /* fsecs / HPET clock */
 unsigned long hpet_tick;                                /* HPET clocks / interrupt */
+static int hpet_use_timer;
 unsigned long vxtime_hz = PIT_TICK_RATE;
 int report_lost_ticks;                          /* command line option */
 unsigned long long monotonic_base;
@@ -105,7 +106,9 @@ static inline unsigned int do_gettimeoffset_tsc(void)
 
 static inline unsigned int do_gettimeoffset_hpet(void)
 {
-        return ((hpet_readl(HPET_COUNTER) - vxtime.last) * vxtime.quot) >> 32;
+        /* cap counter read to one tick to avoid inconsistencies */
+        unsigned long counter = hpet_readl(HPET_COUNTER) - vxtime.last;
+        return (min(counter,hpet_tick) * vxtime.quot) >> 32;
 }
 
 unsigned int (*do_gettimeoffset)(void) = do_gettimeoffset_tsc;
@@ -301,7 +304,7 @@ unsigned long long monotonic_clock(void)
 
                         last_offset = vxtime.last;
                         base = monotonic_base;
-                        this_offset = hpet_readl(HPET_T0_CMP) - hpet_tick;
+                        this_offset = hpet_readl(HPET_COUNTER);
 
                 } while (read_seqretry(&xtime_lock, seq));
                 offset = (this_offset - last_offset);
@@ -377,7 +380,14 @@ static irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
 
         write_seqlock(&xtime_lock);
 
-        if (vxtime.hpet_address) {
+        if (vxtime.hpet_address)
+                offset = hpet_readl(HPET_COUNTER);
+
+        if (hpet_use_timer) {
+                /* if we're using the hpet timer functionality,
+                 * we can more accurately know the counter value
+                 * when the timer interrupt occured.
+                 */
                 offset = hpet_readl(HPET_T0_CMP) - hpet_tick;
                 delay = hpet_readl(HPET_COUNTER) - offset;
         } else {
@@ -803,17 +813,18 @@ static int hpet_timer_stop_set_go(unsigned long tick)
  * Set up timer 0, as periodic with first interrupt to happen at hpet_tick,
  * and period also hpet_tick.
  */
-
-        hpet_writel(HPET_TN_ENABLE | HPET_TN_PERIODIC | HPET_TN_SETVAL |
+        if (hpet_use_timer) {
+                hpet_writel(HPET_TN_ENABLE | HPET_TN_PERIODIC | HPET_TN_SETVAL |
                     HPET_TN_32BIT, HPET_T0_CFG);
-        hpet_writel(hpet_tick, HPET_T0_CMP);
-        hpet_writel(hpet_tick, HPET_T0_CMP); /* AK: why twice? */
-
+                hpet_writel(hpet_tick, HPET_T0_CMP);
+                hpet_writel(hpet_tick, HPET_T0_CMP); /* AK: why twice? */
+                cfg |= HPET_CFG_LEGACY;
+        }
 /*
  * Go!
  */
 
-        cfg |= HPET_CFG_ENABLE | HPET_CFG_LEGACY;
+        cfg |= HPET_CFG_ENABLE;
         hpet_writel(cfg, HPET_CFG);
 
         return 0;
@@ -834,8 +845,7 @@ static int hpet_init(void)
 
         id = hpet_readl(HPET_ID);
 
-        if (!(id & HPET_ID_VENDOR) || !(id & HPET_ID_NUMBER) ||
-            !(id & HPET_ID_LEGSUP))
+        if (!(id & HPET_ID_VENDOR) || !(id & HPET_ID_NUMBER))
                 return -1;
 
         hpet_period = hpet_readl(HPET_PERIOD);
@@ -845,6 +855,8 @@ static int hpet_init(void)
         hpet_tick = (1000000000L * (USEC_PER_SEC / HZ) + hpet_period / 2) /
                 hpet_period;
 
+        hpet_use_timer = (id & HPET_ID_LEGSUP);
+
         return hpet_timer_stop_set_go(hpet_tick);
 }
 
@@ -901,9 +913,11 @@ void __init time_init(void)
         set_normalized_timespec(&wall_to_monotonic,
                                 -xtime.tv_sec, -xtime.tv_nsec);
 
-        if (!hpet_init()) {
+        if (!hpet_init())
                 vxtime_hz = (1000000000000000L + hpet_period / 2) /
                         hpet_period;
+
+        if (hpet_use_timer) {
                 cpu_khz = hpet_calibrate_tsc();
                 timename = "HPET";
 #ifdef CONFIG_X86_PM_TIMER
@@ -968,7 +982,7 @@ void __init time_init_gtod(void)
         if (unsynchronized_tsc())
                 notsc = 1;
         if (vxtime.hpet_address && notsc) {
-                timetype = "HPET";
+                timetype = hpet_use_timer ? "HPET" : "PIT/HPET";
                 vxtime.last = hpet_readl(HPET_T0_CMP) - hpet_tick;
                 vxtime.mode = VXTIME_HPET;
                 do_gettimeoffset = do_gettimeoffset_hpet;
@@ -983,7 +997,7 @@ void __init time_init_gtod(void)
                 printk(KERN_INFO "Disabling vsyscall due to use of PM timer\n");
 #endif
         } else {
-                timetype = vxtime.hpet_address ? "HPET/TSC" : "PIT/TSC";
+                timetype = hpet_use_timer ? "HPET/TSC" : "PIT/TSC";
                 vxtime.mode = VXTIME_TSC;
         }