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Diffstat (limited to 'arch/x86/boot/a20.c')
-rw-r--r--arch/x86/boot/a20.c75
1 files changed, 41 insertions, 34 deletions
diff --git a/arch/x86/boot/a20.c b/arch/x86/boot/a20.c
index 4063d630def..fba8e9c6a50 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
}