x86/apic: Prepare for unifying the interrupt delivery modes setup

There are three places which initialize the interrupt delivery modes:

1) init_bsp_APIC() which is called early might setup the through-local-APIC
   virtual wire mode on non SMP systems.

2) In an SMP-capable system, native_smp_prepare_cpus() tries to switch to
   symmetric I/O model.

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

There is no technical reason to make these initializations at random places
and run the kernel with the potentially wrong mode through the early boot
stage, but it has a problematic side effect: The late switch to symmetric
I/O mode causes dump-capture kernel to hang when the kernel command line
option 'notsc' is active.

Provide a new function to unify that three positions. Preparatory patch to
initialize an interrupt mode directly.
Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: yinghai@kernel.org
Cc: bhe@redhat.com
Link: https://lkml.kernel.org/r/1505293975-26005-3-git-send-email-douly.fnst@cn.fujitsu.com

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

arch/x86/kernel/apic/apic.c

@@ -1319,6 +1319,22 @@ 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;