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[Xen-devel] [PATCH v6 02/12] 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
in an unmatched mode at the beginning of booting time. And it
causes the dump-capture kernel hangs with 'notsc' option inherited
from 1st kernel option.

Provide a new function to unify that three positions. Preparatory
patch to initialize an interrupt mode directly.

Signed-off-by: Dou Liyang <douly.fnst@xxxxxxxxxxxxxx>
 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 bdffcd9..ddc16ff 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 init_bsp_APIC(void);
+extern void apic_intr_mode_init(void);
 extern void setup_local_APIC(void);
 extern void init_apic_mappings(void);
 void register_lapic_address(unsigned long address);
@@ -170,6 +171,7 @@ static inline void disable_local_APIC(void) { }
 # define setup_boot_APIC_clock x86_init_noop
 # define setup_secondary_APIC_clock x86_init_noop
 static inline void lapic_update_tsc_freq(void) { }
+static inline void apic_intr_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 ad5a853..3f22717 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1265,6 +1265,22 @@ void __init init_bsp_APIC(void)
        apic_write(APIC_LVT1, value);
+/* Init the interrupt delivery mode for the BSP */
+void __init apic_intr_mode_init(void)
+       switch (apic_intr_mode_select()) {
+       case APIC_PIC:
+               pr_info("APIC: keep in PIC mode(8259)\n");
+               return;
+       case APIC_VIRTUAL_WIRE:
+               pr_info("APIC: switch to virtual wire mode setup\n");
+               return;
+       case APIC_SYMMETRIC_IO:
+               pr_info("APIC: switch to symmectic I/O mode setup\n");
+               return;
+       }
 static void lapic_setup_esr(void)
        unsigned int oldvalue, value, maxlvt;

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