[PATCH v5 01/12] x86/apic: Construct a selector for the interrupt delivery mode

[Dou Liyang]

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 with 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@xxxxxxxxxxxxxx>
---
 arch/x86/kernel/apic/apic.c | 60 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 2d75faf..88be65e 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1157,6 +1157,66 @@ void __init sync_Arb_IDs(void)
 			APIC_INT_LEVELTRIG | APIC_DM_INIT);
 }
 
+enum apic_intr_mode {
+	APIC_PIC,
+	APIC_VIRTUAL_WIRE,
+	APIC_SYMMETRIC_IO,
+};
+
+static int __init apic_intr_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, Check local APIC only */
+	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("APIC: ACPI MADT or MP tables are not detected\n");
+
+		return APIC_VIRTUAL_WIRE;
+	}
+
+	/* Other checks of APIC options will be done in each setup function */
+
+	return APIC_SYMMETRIC_IO;
+}
+
 /*
  * An initial setup of the virtual wire mode.
  */
-- 
2.5.5