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, 3 insertions, 1 deletions

diff --git a/arch/x86/include/asm/emergency-restart.h b/arch/x86/include/asm/emergency-restart.h
index 94826cf8745..cc70c1c78ca 100644
--- a/arch/x86/include/asm/emergency-restart.h
+++ b/arch/x86/include/asm/emergency-restart.h
@@ -8,7 +8,9 @@ enum reboot_type {
 	BOOT_BIOS = 'b',
 #endif
 	BOOT_ACPI = 'a',
-	BOOT_EFI = 'e'
+	BOOT_EFI = 'e',
+	BOOT_CF9 = 'p',
+	BOOT_CF9_COND = 'q',
 };
 
 extern enum reboot_type reboot_type;