x86: attempt reboot via port CF9 if we have standard PCI ports

Impact: Changes reboot behavior.

If port CF9 seems to be safe to touch, attempt it before trying the
keyboard controller.  Port CF9 is not available on all chipsets (a
significant but decreasing number of modern chipsets don't implement
it), but port CF9 itself should in general be safe to poke (no ill
effects if unimplemented) on any system which has PCI Configuration
Method #1 or #2, as it falls inside the PCI configuration port range
in both cases.  No chipset without PCI is known to have port CF9,
either, although an explicit "pci=bios" would mean we miss this and
therefore don't use port CF9.  An explicit "reboot=pci" can be used to
force the use of port CF9.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 27 insertions, 7 deletions

diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 34f8d37..ddc9389 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -29,14 +29,17 @@ EXPORT_SYMBOL(pm_power_off);
 
 static const struct desc_ptr no_idt = {};
 static int reboot_mode;
-enum reboot_type reboot_type = BOOT_KBD;
+enum reboot_type reboot_type = BOOT_CF9_COND;
 int reboot_force;
 
 #if defined(CONFIG_X86_32) && defined(CONFIG_SMP)
 static int reboot_cpu = -1;
 #endif
 
-/* reboot=b[ios] | s[mp] | t[riple] | k[bd] | e[fi] [, [w]arm | [c]old]
+/* This is set by the PCI code if either type 1 or type 2 PCI is detected */
+bool port_cf9_safe = false;
+
+/* reboot=b[ios] | s[mp] | t[riple] | k[bd] | e[fi] [, [w]arm | [c]old] | p[ci]
    warm   Don't set the cold reboot flag
    cold   Set the cold reboot flag
    bios   Reboot by jumping through the BIOS (only for X86_32)
@@ -45,6 +48,7 @@ static int reboot_cpu = -1;
    kbd    Use the keyboard controller. cold reset (default)
    acpi   Use the RESET_REG in the FADT
    efi    Use efi reset_system runtime service
+   pci    Use the so-called "PCI reset register", CF9
    force  Avoid anything that could hang.
  */
 static int __init reboot_setup(char *str)
@@ -79,6 +83,7 @@ static int __init reboot_setup(char *str)
 		case 'k':
 		case 't':
 		case 'e':
+		case 'p':
 			reboot_type = *str;
 			break;
 
@@ -379,28 +384,43 @@ static void native_machine_emergency_restart(void)
 			load_idt(&no_idt);
 			__asm__ __volatile__("int3");
 
-			reboot_type = BOOT_KBD;
+			reboot_type = BOOT_CF9_COND;
 			break;
 
 #ifdef CONFIG_X86_32
 		case BOOT_BIOS:
 			machine_real_restart(jump_to_bios, sizeof(jump_to_bios));
 
-			reboot_type = BOOT_KBD;
+			reboot_type = BOOT_CF9_COND;
 			break;
 #endif
 
 		case BOOT_ACPI:
 			acpi_reboot();
-			reboot_type = BOOT_KBD;
+			reboot_type = BOOT_CF9_COND;
 			break;
 
-
 		case BOOT_EFI:
 			if (efi_enabled)
-				efi.reset_system(reboot_mode ? EFI_RESET_WARM : EFI_RESET_COLD,
+				efi.reset_system(reboot_mode ?
+						 EFI_RESET_WARM :
+						 EFI_RESET_COLD,
 						 EFI_SUCCESS, 0, NULL);
+			reboot_type = BOOT_CF9_COND;
+			break;
+
+		case BOOT_CF9:
+			port_cf9_safe = true;
+			/* fall through */
 
+		case BOOT_CF9_COND:
+			if (port_cf9_safe) {
+				u8 cf9 = inb(0xcf9) & ~6;
+				outb(cf9|2, 0xcf9); /* Request hard reset */
+				udelay(50);
+				outb(cf9|6, 0xcf9); /* Actually do the reset */
+				udelay(50);
+			}
 			reboot_type = BOOT_KBD;
 			break;
 		}