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x86/apic, doc: Justification for disabling IO APIC before Local APIC

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Since erratum AVR31 in "Intel Atom Processor C2000 Product Family
Specification Update" is now published, I added a justification
comment for disabling IO APIC before Local APIC, as changed in commit:

522e664644 x86/apic: Disable I/O APIC before shutdown of the local APIC

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1386202069-51515-1-git-send-email-fenghua.yu@intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Fenghua Yu 2013-12-04 16:07:49 -08:00 committed by H. Peter Anvin
parent e0f6dec35f
commit 2885432aaf
1 changed files with 11 additions and 0 deletions
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11
arch/x86/kernel/reboot.c
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@ -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