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-rw-r--r--arch/x86/kernel/hpet.c24
1 files changed, 24 insertions, 0 deletions
diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index ad2b15a1334..59fd3b6b130 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;