[Xen-devel] [PATCH v6 01/12] x86/apic: Construct a selector for the interrupt delivery mode

[Dou Liyang <douly.fnst@xxxxxxxxxxxxxx>]

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 | 59 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 2d75faf..ad5a853 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1157,6 +1157,65 @@ 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 separate chip ? */
+       if (!boot_cpu_has(X86_FEATURE_APIC) && !smp_found_config) {
+               disable_apic = 1;
+
+               return APIC_PIC;
+       }
+
+       /* 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;
+       }
+#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;
+       }
+
+       return APIC_SYMMETRIC_IO;
+}
+
 /*
  * An initial setup of the virtual wire mode.
  */
-- 
2.5.5




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