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>

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 11358df..fa77be8 100644 (file)
--- 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);