Merge branch 'linus' into x86/tracehook

1 files changed, 24 insertions, 0 deletions

diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index ad2b15a1334d..59fd3b6b1303 100644
--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -359,6 +359,7 @@ static int hpet_clocksource_register(void)
 int __init hpet_enable(void)
 {
         unsigned long id;
+        int i;
 
         if (!is_hpet_capable())
                 return 0;
@@ -369,6 +370,29 @@ int __init hpet_enable(void)
          * Read the period and check for a sane value:
          */
         hpet_period = hpet_readl(HPET_PERIOD);
+
+        /*
+         * AMD SB700 based systems with spread spectrum enabled use a
+         * SMM based HPET emulation to provide proper frequency
+         * setting. The SMM code is initialized with the first HPET
+         * register access and takes some time to complete. During
+         * this time the config register reads 0xffffffff. We check
+         * for max. 1000 loops whether the config register reads a non
+         * 0xffffffff value to make sure that HPET is up and running
+         * before we go further. A counting loop is safe, as the HPET
+         * access takes thousands of CPU cycles. On non SB700 based
+         * machines this check is only done once and has no side
+         * effects.
+         */
+        for (i = 0; hpet_readl(HPET_CFG) == 0xFFFFFFFF; i++) {
+                if (i == 1000) {
+                        printk(KERN_WARNING
+                               "HPET config register value = 0xFFFFFFFF. "
+                               "Disabling HPET\n");
+                        goto out_nohpet;
+                }
+        }
+
         if (hpet_period < HPET_MIN_PERIOD || hpet_period > HPET_MAX_PERIOD)
                 goto out_nohpet;