1 files changed, 41 insertions, 34 deletions

diff --git a/arch/x86/boot/a20.c b/arch/x86/boot/a20.c
index 4063d630deff..fba8e9c6a504 100644
--- a/arch/x86/boot/a20.c
+++ b/arch/x86/boot/a20.c
@@ -2,6 +2,7 @@
  *
  *   Copyright (C) 1991, 1992 Linus Torvalds
  *   Copyright 2007-2008 rPath, Inc. - All Rights Reserved
+ *   Copyright 2009 Intel Corporation
  *
  *   This file is part of the Linux kernel, and is made available under
  *   the terms of the GNU General Public License version 2.
@@ -15,16 +16,23 @@
 #include "boot.h"
 
 #define MAX_8042_LOOPS  100000
+#define MAX_8042_FF     32
 
 static int empty_8042(void)
 {
         u8 status;
         int loops = MAX_8042_LOOPS;
+        int ffs   = MAX_8042_FF;
 
         while (loops--) {
                 io_delay();
 
                 status = inb(0x64);
+                if (status == 0xff) {
+                        /* FF is a plausible, but very unlikely status */
+                        if (!--ffs)
+                                return -1; /* Assume no KBC present */
+                }
                 if (status & 1) {
                         /* Read and discard input data */
                         io_delay();
@@ -118,44 +126,43 @@ static void enable_a20_fast(void)
 
 int enable_a20(void)
 {
-#if defined(CONFIG_X86_ELAN)
-        /* Elan croaks if we try to touch the KBC */
-        enable_a20_fast();
-        while (!a20_test_long())
-                ;
-        return 0;
-#elif defined(CONFIG_X86_VOYAGER)
+#ifdef CONFIG_X86_VOYAGER
         /* On Voyager, a20_test() is unsafe? */
         enable_a20_kbc();
         return 0;
 #else
        int loops = A20_ENABLE_LOOPS;
-        while (loops--) {
-                /* First, check to see if A20 is already enabled
-                   (legacy free, etc.) */
-                if (a20_test_short())
-                        return 0;
-
-                /* Next, try the BIOS (INT 0x15, AX=0x2401) */
-                enable_a20_bios();
-                if (a20_test_short())
-                        return 0;
-
-                /* Try enabling A20 through the keyboard controller */
-                empty_8042();
-                if (a20_test_short())
-                        return 0; /* BIOS worked, but with delayed reaction */
-
-                enable_a20_kbc();
-                if (a20_test_long())
-                        return 0;
-
-                /* Finally, try enabling the "fast A20 gate" */
-                enable_a20_fast();
-                if (a20_test_long())
-                        return 0;
-        }
-
-        return -1;
+       int kbc_err;
+
+       while (loops--) {
+               /* First, check to see if A20 is already enabled
+                  (legacy free, etc.) */
+               if (a20_test_short())
+                       return 0;
+               
+               /* Next, try the BIOS (INT 0x15, AX=0x2401) */
+               enable_a20_bios();
+               if (a20_test_short())
+                       return 0;
+               
+               /* Try enabling A20 through the keyboard controller */
+               kbc_err = empty_8042();
+
+               if (a20_test_short())
+                       return 0; /* BIOS worked, but with delayed reaction */
+        
+               if (!kbc_err) {
+                       enable_a20_kbc();
+                       if (a20_test_long())
+                               return 0;
+               }
+               
+               /* Finally, try enabling the "fast A20 gate" */
+               enable_a20_fast();
+               if (a20_test_long())
+                       return 0;
+       }
+       
+       return -1;
 #endif
 }