x86/apic, doc: Justification for disabling IO APIC before Local APIC (2885432a) · Commits · e / devices / android_kernel_fairphone_FP3

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: 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>

arch/x86/kernel/reboot.c

+11 −0

Original line number	Diff line number	Diff line
		@@ -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