Commit 2885432a authored by Fenghua Yu's avatar Fenghua Yu Committed by H. Peter Anvin

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

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:

522e6646 x86/apic: Disable I/O APIC before shutdown of the local APIC
Signed-off-by: default avatarFenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1386202069-51515-1-git-send-email-fenghua.yu@intel.comSigned-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent e0f6dec3
...@@ -558,6 +558,17 @@ void native_machine_shutdown(void) ...@@ -558,6 +558,17 @@ void native_machine_shutdown(void)
{ {
/* Stop the cpus and apics */ /* Stop the cpus and apics */
#ifdef CONFIG_X86_IO_APIC #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(); disable_IO_APIC();
#endif #endif
......
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