1 files changed, 17 insertions, 14 deletions

diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index 351f9c0fea1f..410fdb3f1939 100644
--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -35,7 +35,6 @@
 unsigned long                           hpet_address;
 u8                                      hpet_blockid; /* OS timer block num */
 u8                                      hpet_msi_disable;
-u8                                      hpet_readback_cmp;
 
 #ifdef CONFIG_PCI_MSI
 static unsigned long                    hpet_num_timers;
@@ -395,23 +394,27 @@ static int hpet_next_event(unsigned long delta,
          * at that point and we would wait for the next hpet interrupt
          * forever. We found out that reading the CMP register back
          * forces the transfer so we can rely on the comparison with
-         * the counter register below.
+         * the counter register below. If the read back from the
+         * compare register does not match the value we programmed
+         * then we might have a real hardware problem. We can not do
+         * much about it here, but at least alert the user/admin with
+         * a prominent warning.
          *
-         * That works fine on those ATI chipsets, but on newer Intel
-         * chipsets (ICH9...) this triggers due to an erratum: Reading
-         * the comparator immediately following a write is returning
-         * the old value.
+         * An erratum on some chipsets (ICH9,..), results in
+         * comparator read immediately following a write returning old
+         * value. Workaround for this is to read this value second
+         * time, when first read returns old value.
          *
-         * We restrict the read back to the affected ATI chipsets (set
-         * by quirks) and also run it with hpet=verbose for debugging
-         * purposes.
+         * In fact the write to the comparator register is delayed up
+         * to two HPET cycles so the workaround we tried to restrict
+         * the readback to those known to be borked ATI chipsets
+         * failed miserably. So we give up on optimizations forever
+         * and penalize all HPET incarnations unconditionally.
          */
-        if (hpet_readback_cmp || hpet_verbose) {
-                u32 cmp = hpet_readl(HPET_Tn_CMP(timer));
-
-                if (cmp != cnt)
+        if (unlikely((u32)hpet_readl(HPET_Tn_CMP(timer)) != cnt)) {
+                if (hpet_readl(HPET_Tn_CMP(timer)) != cnt)
                         printk_once(KERN_WARNING
-                            "hpet: compare register read back failed.\n");
+                                "hpet: compare register read back failed.\n");
         }
 
         return (s32)(hpet_readl(HPET_COUNTER) - cnt) >= 0 ? -ETIME : 0;