x86/apic: Refine enable_IR_x2apic() and related functions

Refine enable_IR_x2apic() and related functions for better readability.

[ tglx: Removed the XAPIC mode change and split it out into a seperate
  	patch. Added comments. ]

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: iommu@lists.linux-foundation.org
Cc: H. Peter Anvin <hpa@linux.intel.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: David Rientjes <rientjes@google.com>
Cc: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
Cc: Jan Beulich <JBeulich@suse.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Oren Twaig <oren@scalemp.com>
Link: http://lkml.kernel.org/r/1420615903-28253-8-git-send-email-jiang.liu@linux.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 47 insertions, 45 deletions

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 11358df3bd08..fa77be8d0b17 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1573,7 +1573,7 @@ void enable_x2apic(void)
 }
 #endif /* CONFIG_X86_X2APIC */
 
-int __init enable_IR(void)
+static int __init try_to_enable_IR(void)
 {
 #ifdef CONFIG_IRQ_REMAP
         if (!irq_remapping_supported()) {
@@ -1586,17 +1586,51 @@ int __init enable_IR(void)
                         "io-apic setup\n");
                 return -1;
         }
-
+#endif
         return irq_remapping_enable();
+}
+
+static __init void try_to_enable_x2apic(int ir_stat)
+{
+#ifdef CONFIG_X86_X2APIC
+        if (!x2apic_supported())
+                return;
+
+        if (ir_stat < 0) {
+                /* IR is required if there is APIC ID > 255 even when running
+                 * under KVM
+                 */
+                if (max_physical_apicid > 255 ||
+                    !hypervisor_x2apic_available()) {
+                        pr_info("IRQ remapping doesn't support X2APIC mode, disable x2apic.\n");
+                        if (x2apic_preenabled)
+                                disable_x2apic();
+                        return;
+                }
+
+                /*
+                 * without IR all CPUs can be addressed by IOAPIC/MSI
+                 * only in physical mode
+                 */
+                x2apic_force_phys();
+
+        } else if (ir_stat == IRQ_REMAP_XAPIC_MODE) {
+                pr_info("x2apic not enabled, IRQ remapping is in xapic mode\n");
+                return;
+        }
+
+        if (!x2apic_mode) {
+                x2apic_mode = 1;
+                enable_x2apic();
+                pr_info("Enabled x2apic\n");
+        }
 #endif
-        return -1;
 }
 
 void __init enable_IR_x2apic(void)
 {
         unsigned long flags;
-        int ret;
-        int hardware_init_ret;
+        int ret, ir_stat;
 
         if (!IS_ENABLED(CONFIG_X86_X2APIC)) {
                 u64 msr;
@@ -1606,8 +1640,8 @@ void __init enable_IR_x2apic(void)
                         panic("BIOS has enabled x2apic but kernel doesn't support x2apic, please disable x2apic in BIOS.\n");
         }
 
-        hardware_init_ret = irq_remapping_prepare();
-        if (hardware_init_ret && !x2apic_supported())
+        ir_stat = irq_remapping_prepare();
+        if (ir_stat < 0 && !x2apic_supported())
                 return;
 
         ret = save_ioapic_entries();
@@ -1622,45 +1656,13 @@ void __init enable_IR_x2apic(void)
 
         if (x2apic_preenabled && nox2apic)
                 disable_x2apic();
+        /* If irq_remapping_prepare() succeded, try to enable it */
+        if (ir_stat >= 0)
+                ir_stat = try_to_enable_IR();
+        /* ir_stat contains the remap mode or an error code */
+        try_to_enable_x2apic(ir_stat);
 
-        if (hardware_init_ret)
-                ret = -1;
-        else
-                ret = enable_IR();
-
-        if (!x2apic_supported())
-                goto skip_x2apic;
-
-        if (ret < 0) {
-                /* IR is required if there is APIC ID > 255 even when running
-                 * under KVM
-                 */
-                if (max_physical_apicid > 255 ||
-                    !hypervisor_x2apic_available()) {
-                        if (x2apic_preenabled)
-                                disable_x2apic();
-                        goto skip_x2apic;
-                }
-                /*
-                 * without IR all CPUs can be addressed by IOAPIC/MSI
-                 * only in physical mode
-                 */
-                x2apic_force_phys();
-        }
-
-        if (ret == IRQ_REMAP_XAPIC_MODE) {
-                pr_info("x2apic not enabled, IRQ remapping is in xapic mode\n");
-                goto skip_x2apic;
-        }
-
-        if (x2apic_supported() && !x2apic_mode) {
-                x2apic_mode = 1;
-                enable_x2apic();
-                pr_info("Enabled x2apic\n");
-        }
-
-skip_x2apic:
-        if (ret < 0) /* IR enabling failed */
+        if (ir_stat < 0)
                 restore_ioapic_entries();
         legacy_pic->restore_mask();
         local_irq_restore(flags);