diff options
Diffstat (limited to 'arch/x86/boot/a20.c')
| -rw-r--r-- | arch/x86/boot/a20.c | 75 |
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 } |