1 files changed, 17 insertions, 1 deletions

diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index 3f0019e0a229..81408b93f887 100644
--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -236,6 +236,10 @@ static void hpet_stop_counter(void)
         unsigned long cfg = hpet_readl(HPET_CFG);
         cfg &= ~HPET_CFG_ENABLE;
         hpet_writel(cfg, HPET_CFG);
+}
+
+static void hpet_reset_counter(void)
+{
         hpet_writel(0, HPET_COUNTER);
         hpet_writel(0, HPET_COUNTER + 4);
 }
@@ -250,6 +254,7 @@ static void hpet_start_counter(void)
 static void hpet_restart_counter(void)
 {
         hpet_stop_counter();
+        hpet_reset_counter();
         hpet_start_counter();
 }
 
@@ -309,7 +314,7 @@ static int hpet_setup_msi_irq(unsigned int irq);
 static void hpet_set_mode(enum clock_event_mode mode,
                           struct clock_event_device *evt, int timer)
 {
-        unsigned long cfg;
+        unsigned long cfg, cmp, now;
         uint64_t delta;
 
         switch (mode) {
@@ -317,12 +322,23 @@ static void hpet_set_mode(enum clock_event_mode mode,
                 hpet_stop_counter();
                 delta = ((uint64_t)(NSEC_PER_SEC/HZ)) * evt->mult;
                 delta >>= evt->shift;
+                now = hpet_readl(HPET_COUNTER);
+                cmp = now + (unsigned long) delta;
                 cfg = hpet_readl(HPET_Tn_CFG(timer));
                 /* Make sure we use edge triggered interrupts */
                 cfg &= ~HPET_TN_LEVEL;
                 cfg |= HPET_TN_ENABLE | HPET_TN_PERIODIC |
                        HPET_TN_SETVAL | HPET_TN_32BIT;
                 hpet_writel(cfg, HPET_Tn_CFG(timer));
+                hpet_writel(cmp, HPET_Tn_CMP(timer));
+                udelay(1);
+                /*
+                 * HPET on AMD 81xx needs a second write (with HPET_TN_SETVAL
+                 * cleared) to T0_CMP to set the period. The HPET_TN_SETVAL
+                 * bit is automatically cleared after the first write.
+                 * (See AMD-8111 HyperTransport I/O Hub Data Sheet,
+                 * Publication # 24674)
+                 */
                 hpet_writel((unsigned long) delta, HPET_Tn_CMP(timer));
                 hpet_start_counter();
                 hpet_print_config();