2 files changed, 44 insertions, 42 deletions

diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 654b46574b91..3399d3a99730 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -114,8 +114,8 @@ EXPORT_SYMBOL(machine_real_restart);
  */
 static int __init set_pci_reboot(const struct dmi_system_id *d)
 {
-        if (reboot_type != BOOT_CF9) {
-                reboot_type = BOOT_CF9;
+        if (reboot_type != BOOT_CF9_FORCE) {
+                reboot_type = BOOT_CF9_FORCE;
                 pr_info("%s series board detected. Selecting %s-method for reboots.\n",
                         d->ident, "PCI");
         }
@@ -458,20 +458,23 @@ void __attribute__((weak)) mach_reboot_fixups(void)
 }
 
 /*
- * Windows compatible x86 hardware expects the following on reboot:
+ * To the best of our knowledge Windows compatible x86 hardware expects
+ * the following on reboot:
  *
  * 1) If the FADT has the ACPI reboot register flag set, try it
  * 2) If still alive, write to the keyboard controller
  * 3) If still alive, write to the ACPI reboot register again
  * 4) If still alive, write to the keyboard controller again
  * 5) If still alive, call the EFI runtime service to reboot
- * 6) If still alive, write to the PCI IO port 0xCF9 to reboot
- * 7) If still alive, inform BIOS to do a proper reboot
+ * 6) If no EFI runtime service, call the BIOS to do a reboot
  *
- * If the machine is still alive at this stage, it gives up. We default to
- * following the same pattern, except that if we're still alive after (7) we'll
- * try to force a triple fault and then cycle between hitting the keyboard
- * controller and doing that
+ * We default to following the same pattern. We also have
+ * two other reboot methods: 'triple fault' and 'PCI', which
+ * can be triggered via the reboot= kernel boot option or
+ * via quirks.
+ *
+ * This means that this function can never return, it can misbehave
+ * by not rebooting properly and hanging.
  */
 static void native_machine_emergency_restart(void)
 {
@@ -492,6 +495,11 @@ static void native_machine_emergency_restart(void)
         for (;;) {
                 /* Could also try the reset bit in the Hammer NB */
                 switch (reboot_type) {
+                case BOOT_ACPI:
+                        acpi_reboot();
+                        reboot_type = BOOT_KBD;
+                        break;
+
                 case BOOT_KBD:
                         mach_reboot_fixups(); /* For board specific fixups */
 
@@ -509,43 +517,29 @@ static void native_machine_emergency_restart(void)
                         }
                         break;
 
-                case BOOT_TRIPLE:
-                        load_idt(&no_idt);
-                        __asm__ __volatile__("int3");
-
-                        /* We're probably dead after this, but... */
-                        reboot_type = BOOT_KBD;
-                        break;
-
-                case BOOT_BIOS:
-                        machine_real_restart(MRR_BIOS);
-
-                        /* We're probably dead after this, but... */
-                        reboot_type = BOOT_TRIPLE;
-                        break;
-
-                case BOOT_ACPI:
-                        acpi_reboot();
-                        reboot_type = BOOT_KBD;
-                        break;
-
                 case BOOT_EFI:
                         if (efi_enabled(EFI_RUNTIME_SERVICES))
                                 efi.reset_system(reboot_mode == REBOOT_WARM ?
                                                  EFI_RESET_WARM :
                                                  EFI_RESET_COLD,
                                                  EFI_SUCCESS, 0, NULL);
-                        reboot_type = BOOT_CF9_COND;
+                        reboot_type = BOOT_BIOS;
+                        break;
+
+                case BOOT_BIOS:
+                        machine_real_restart(MRR_BIOS);
+
+                        /* We're probably dead after this, but... */
+                        reboot_type = BOOT_CF9_SAFE;
                         break;
 
-                case BOOT_CF9:
+                case BOOT_CF9_FORCE:
                         port_cf9_safe = true;
                         /* Fall through */
 
-                case BOOT_CF9_COND:
+                case BOOT_CF9_SAFE:
                         if (port_cf9_safe) {
-                                u8 reboot_code = reboot_mode == REBOOT_WARM ?
-                                        0x06 : 0x0E;
+                                u8 reboot_code = reboot_mode == REBOOT_WARM ?  0x06 : 0x0E;
                                 u8 cf9 = inb(0xcf9) & ~reboot_code;
                                 outb(cf9|2, 0xcf9); /* Request hard reset */
                                 udelay(50);
@@ -553,7 +547,15 @@ static void native_machine_emergency_restart(void)
                                 outb(cf9|reboot_code, 0xcf9);
                                 udelay(50);
                         }
-                        reboot_type = BOOT_BIOS;
+                        reboot_type = BOOT_TRIPLE;
+                        break;
+
+                case BOOT_TRIPLE:
+                        load_idt(&no_idt);
+                        __asm__ __volatile__("int3");
+
+                        /* We're probably dead after this, but... */
+                        reboot_type = BOOT_KBD;
                         break;
                 }
         }
diff --git a/include/linux/reboot.h b/include/linux/reboot.h
index 9e7db9e73cc1..48bf152761c7 100644
--- a/include/linux/reboot.h
+++ b/include/linux/reboot.h
@@ -20,13 +20,13 @@ enum reboot_mode {
 extern enum reboot_mode reboot_mode;
 
 enum reboot_type {
-        BOOT_TRIPLE = 't',
-        BOOT_KBD = 'k',
-        BOOT_BIOS = 'b',
-        BOOT_ACPI = 'a',
-        BOOT_EFI = 'e',
-        BOOT_CF9 = 'p',
-        BOOT_CF9_COND = 'q',
+        BOOT_TRIPLE     = 't',
+        BOOT_KBD        = 'k',
+        BOOT_BIOS       = 'b',
+        BOOT_ACPI       = 'a',
+        BOOT_EFI        = 'e',
+        BOOT_CF9_FORCE  = 'p',
+        BOOT_CF9_SAFE   = 'q',
 };
 extern enum reboot_type reboot_type;