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Subject[RFC PATCH v3 03/12] x86/apic: Prepare for unifying the interrupt delivery modes setup
There are three positions for initializing the interrupt delivery

1) In IRQ initial function, may setup the through-local-APIC
virtual wire mode.

2) In an SMP-capable system, will try to switch to symmetric I/O
model when preparing the cpus in native_smp_prepare_cpus().

3) In UP system with UP_LATE_INIT=y, will set up local APIC and
I/O APIC in smp_init().

Switching to symmetric I/O mode is so late, which causes kernel
is in a mismatched mode at the beginning of booting time. And it
causes the dump-capture kernel hangs with 'notsc' option inherited
from 1st kernel option.

Preparatory patch to initialize an interrupt mode directly and provide
a new function apic_interrupt_mode_init() to unify that three positions
and do that setup as soon as possible.

Signed-off-by: Dou Liyang <>
v2 --> v3:
change the function name from init_interrupt_mode to

arch/x86/include/asm/apic.h | 2 ++
arch/x86/kernel/apic/apic.c | 16 ++++++++++++++++
2 files changed, 18 insertions(+)

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index 4f4519b..e9502e6 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -128,6 +128,7 @@ extern void disable_local_APIC(void);
extern void lapic_shutdown(void);
extern void sync_Arb_IDs(void);
extern void apic_virtual_wire_mode_setup(void);
+extern void apic_interrupt_mode_init(void);
extern void setup_local_APIC(void);
extern void init_apic_mappings(void);
void register_lapic_address(unsigned long address);
@@ -171,6 +172,7 @@ static inline void disable_local_APIC(void) { }
# define setup_secondary_APIC_clock x86_init_noop
static inline void lapic_update_tsc_freq(void) { }
static inline void apic_virtual_wire_mode_setup(void) {}
+static inline void apic_interrupt_mode_init(void) {}
#endif /* !CONFIG_X86_LOCAL_APIC */

#ifdef CONFIG_X86_X2APIC
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 3342f144..56be7f3 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1267,6 +1267,22 @@ void __init apic_virtual_wire_mode_setup(void)
apic_write(APIC_LVT1, value);

+/* Init the interrupt delivery mode for the BSP */
+void __init apic_interrupt_mode_init(void)
+ switch (apic_interrupt_mode_select()) {
+ case APIC_PIC:
+ pr_info("Keep in PIC mode(8259)\n");
+ return;
+ pr_info("Switch to virtual wire mode\n");
+ return;
+ pr_info("Switch to symmectic I/O mode\n");
+ return;
+ }
static void lapic_setup_esr(void)
unsigned int oldvalue, value, maxlvt;

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