linux-kernel - [PATCH] x86: Do not try to disable hpet if it hasn't been initialized before

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Date:	Thu, 22 Jul 2010 16:22:42 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>
CC:	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Venkatesh Pallipadi <venki@...gle.com>
Subject: [PATCH] x86: Do not try to disable hpet if it hasn't been initialized
 before

[ x86 folk: While this patch is just a generic x86 bugfix, it really only affects
  the Xen pv-on-hvm patch series that I'm going to post shortly.  Do you want to
  commit it separately via tip.git, or are you OK with me sending it to Linus
  directly? - J ]

hpet_disable is called unconditionally on machine reboot if hpet support
is compiled in the kernel.
hpet_disable only checks if the machine is hpet capable but doesn't make
sure that hpet has been initialized.

Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
Acked-by: Venkatesh Pallipadi <venki@...gle.com>

diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index a198b7c..9e90dac 100644
--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -964,16 +964,18 @@ fs_initcall(hpet_late_init);
 
 void hpet_disable(void)
 {
-	if (is_hpet_capable()) {
-		unsigned int cfg = hpet_readl(HPET_CFG);
+	unsigned int cfg;
 
-		if (hpet_legacy_int_enabled) {
-			cfg &= ~HPET_CFG_LEGACY;
-			hpet_legacy_int_enabled = 0;
-		}
-		cfg &= ~HPET_CFG_ENABLE;
-		hpet_writel(cfg, HPET_CFG);
+	if (!is_hpet_capable() || !hpet_address || !hpet_virt_address)
+		return;
+
+	cfg = hpet_readl(HPET_CFG);
+	if (hpet_legacy_int_enabled) {
+		cfg &= ~HPET_CFG_LEGACY;
+		hpet_legacy_int_enabled = 0;
 	}
+	cfg &= ~HPET_CFG_ENABLE;
+	hpet_writel(cfg, HPET_CFG);
 }
 
 #ifdef CONFIG_HPET_EMULATE_RTC


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