diff options
authorFenghua Yu <fenghua.yu@intel.com>2013-12-04 16:07:49 -0800
committerH. Peter Anvin <hpa@linux.intel.com>2013-12-04 19:33:21 -0800
commit2885432aaf15c1b7e65c787bfe7c5fec428296f0 (patch)
parente0f6dec35f9286e78879fe1ac92803fd69fc4fdc (diff)
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: 522e66464467 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>
1 files changed, 11 insertions, 0 deletions
diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index da3c599584a3..c752cb43e52f 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 */
+ /*
+ * 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.
+ */