From a6825f1c1fa83b1e92b6715ee5771a4d6524d3b9 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Thu, 14 Aug 2008 12:17:06 +0200 Subject: [PATCH] x86: hpet: workaround SB700 BIOS 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. Based on a quirk patch from: crane cai Signed-off-by: Thomas Gleixner --- arch/x86/kernel/hpet.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) 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; -- 2.20.1