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From: "Fenghua Yu" <fenghua.yu@intel.com>
To: "Ingo Molnar" <mingo@elte.hu>,
	"H. Peter Anvin" <hpa@linux.intel.com>,
	"Thomas Gleixner" <tglx@linutronix.de>
Cc: "linux-kernel" <linux-kernel@vger.kernel.org>,
	"x86" <x86@kernel.org>, "Fenghua Yu" <fenghua.yu@intel.com>
Subject: [PATCH] x86/apic: Justification for disabling IO APIC before Local APIC
Date: Wed,  4 Dec 2013 16:07:49 -0800
Message-ID: <1386202069-51515-1-git-send-email-fenghua.yu@intel.com> (raw)

From: Fenghua Yu <fenghua.yu@intel.com>

Since erratum AVR31 in "Intel Atom Processor C2000 Product Family
Specification Update" is published, I add a justification comment for
disabling IO APIC before Local APIC (commit 522e6646).

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
---
 arch/x86/kernel/reboot.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index da3c599..c752cb4 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -558,6 +558,17 @@ void native_machine_shutdown(void)
 {
 	/* Stop the cpus and apics */
 #ifdef CONFIG_X86_IO_APIC
+	/*
+	 * Disabling IO APIC before local APIC is a workaround for
+	 * erratum AVR31 in "Intel Atom Processor C2000 Product Family
+	 * Specification Update". In this situation, interrupts that target
+	 * a Logical Processor whose Local APIC is either in the process of
+	 * being hardware disabled or software disabled are neither delivered
+	 * nor discarded. When this erratum occurs, the processor may hang.
+	 *
+	 * Even without the erratum, it still makes sense to quiet IO APIC
+	 * before disabling Local APIC.
+	 */
 	disable_IO_APIC();
 #endif
 
-- 
1.8.1.2


             reply index

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-12-05  0:07 Fenghua Yu [this message]
2013-12-05  3:36 ` [tip:x86/urgent] x86/apic, doc: " tip-bot for Fenghua Yu
2013-12-05  8:54 ` [PATCH] x86/apic: " Ingo Molnar
2013-12-05 13:27   ` Yu, Fenghua

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