[RFC PATCH v3 02/12] x86/apic: Construct a selector for the interrupt delivery mode

[Dou Liyang <douly.fnst@cn.fujitsu.com>]

Now, there are many switches in kernel which are used to determine
the final interrupt delivery mode, as shown below:

1) kconfig:
   CONFIG_X86_64; CONFIG_X86_LOCAL_APIC; CONFIG_x86_IO_APIC
2) kernel option: disable_apic; skip_ioapic_setup
3) CPU Capability: boot_cpu_has(X86_FEATURE_APIC)
4) MP table: smp_found_config
5) ACPI: acpi_lapic; acpi_ioapic; nr_ioapic

These switches are disordered and scattered and there are also some
dependencies between each other. These make the code difficult to
maintain and read.

Construct a selector to unify them into a single function, then,
Use this selector to get an interrupt delivery mode directly.

Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
---
The selector logic:
       +------------+
       |disable_apic+--------------------+
       +------------+       true         |
              |false                     |
              |                          |
 +------------v------------------+       |
 |!boot_cpu_has(X86_FEATURE_APIC)+-------+
 +-------------------------------+  true |
              |false                     |
              |                          |
      +-------v---------+                v
      |!smp_found_config|            PIC MODE
      +---------------+-+
       |false         |true
       |              |
       v          +---v---------+
SYMMETRIC IO MODE | !acpi_lapic |
                  +------+------+
                         |
                         v
                   VIRTUAL WIRE MODE 
v2 --> v3:
  modify some comments.
 arch/x86/kernel/apic/apic.c | 61 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 6bf7249..3342f144 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1157,6 +1157,67 @@ void __init sync_Arb_IDs(void)
 			APIC_INT_LEVELTRIG | APIC_DM_INIT);
 }
 
+enum apic_interrupt_mode {
+	APIC_PIC = 0,
+	APIC_VIRTUAL_WIRE,
+	APIC_SYMMETRIC_IO,
+	APIC_MODE_COUNT
+};
+
+static int __init apic_interrupt_mode_select(void)
+{
+	/* Check kernel option */
+	if (disable_apic) {
+		pr_info("APIC disabled via kernel command line\n");
+		return APIC_PIC;
+	}
+
+	/* Check BIOS */
+#ifdef CONFIG_X86_64
+	/* On 64-bit, the APIC must be integrated */
+	if (!boot_cpu_has(X86_FEATURE_APIC)) {
+		disable_apic = 1;
+		pr_info("APIC disabled by BIOS\n");
+		return APIC_PIC;
+	}
+#else
+	/*
+	 * On 32-bit, check whether there is a separate chip or integrated
+	 * APIC
+	 */
+
+	/* Has a local APIC ? */
+	if (!boot_cpu_has(X86_FEATURE_APIC) &&
+		APIC_INTEGRATED(boot_cpu_apic_version)) {
+		disable_apic = 1;
+		pr_err(FW_BUG "Local APIC %d not detected, force emulation\n",
+				       boot_cpu_physical_apicid);
+		return APIC_PIC;
+	}
+
+	/* Has a separate chip ? */
+	if (!boot_cpu_has(X86_FEATURE_APIC) && !smp_found_config) {
+		disable_apic = 1;
+
+		return APIC_PIC;
+	}
+#endif
+
+	/* Check MP table or ACPI MADT configuration */
+	if (!smp_found_config) {
+		disable_ioapic_support();
+
+		if (!acpi_lapic)
+			pr_info("ACPI MADT or MP table not detected\n");
+
+		return APIC_VIRTUAL_WIRE;
+	}
+
+	/* Other checks of APIC options will be done in each setup function */
+
+	return APIC_SYMMETRIC_IO;
+}
+
 /*
  * Setup the through-local-APIC virtual wire mode.
  */
-- 
2.5.5