blob: fba8e9c6a504edd049d2dcad7bca7938469f5578 [file] [log] [blame]
H. Peter Anvin5a8a8122007-07-11 12:18:42 -07001/* -*- linux-c -*- ------------------------------------------------------- *
2 *
3 * Copyright (C) 1991, 1992 Linus Torvalds
H. Peter Anvinaa60d132008-06-27 13:23:00 -07004 * Copyright 2007-2008 rPath, Inc. - All Rights Reserved
H. Peter Anvin3bd323a2009-02-02 14:52:00 -08005 * Copyright 2009 Intel Corporation
H. Peter Anvin5a8a8122007-07-11 12:18:42 -07006 *
7 * This file is part of the Linux kernel, and is made available under
8 * the terms of the GNU General Public License version 2.
9 *
10 * ----------------------------------------------------------------------- */
11
12/*
H. Peter Anvin5a8a8122007-07-11 12:18:42 -070013 * Enable A20 gate (return -1 on failure)
14 */
15
16#include "boot.h"
17
18#define MAX_8042_LOOPS 100000
H. Peter Anvin3bd323a2009-02-02 14:52:00 -080019#define MAX_8042_FF 32
H. Peter Anvin5a8a8122007-07-11 12:18:42 -070020
21static int empty_8042(void)
22{
23 u8 status;
24 int loops = MAX_8042_LOOPS;
H. Peter Anvin3bd323a2009-02-02 14:52:00 -080025 int ffs = MAX_8042_FF;
H. Peter Anvin5a8a8122007-07-11 12:18:42 -070026
27 while (loops--) {
28 io_delay();
29
30 status = inb(0x64);
H. Peter Anvin3bd323a2009-02-02 14:52:00 -080031 if (status == 0xff) {
32 /* FF is a plausible, but very unlikely status */
33 if (!--ffs)
34 return -1; /* Assume no KBC present */
35 }
H. Peter Anvin5a8a8122007-07-11 12:18:42 -070036 if (status & 1) {
37 /* Read and discard input data */
38 io_delay();
39 (void)inb(0x60);
40 } else if (!(status & 2)) {
41 /* Buffers empty, finished! */
42 return 0;
43 }
44 }
45
46 return -1;
47}
48
49/* Returns nonzero if the A20 line is enabled. The memory address
50 used as a test is the int $0x80 vector, which should be safe. */
51
52#define A20_TEST_ADDR (4*0x80)
53#define A20_TEST_SHORT 32
54#define A20_TEST_LONG 2097152 /* 2^21 */
55
56static int a20_test(int loops)
57{
58 int ok = 0;
59 int saved, ctr;
60
61 set_fs(0x0000);
62 set_gs(0xffff);
63
64 saved = ctr = rdfs32(A20_TEST_ADDR);
65
66 while (loops--) {
67 wrfs32(++ctr, A20_TEST_ADDR);
68 io_delay(); /* Serialize and make delay constant */
69 ok = rdgs32(A20_TEST_ADDR+0x10) ^ ctr;
70 if (ok)
71 break;
72 }
73
74 wrfs32(saved, A20_TEST_ADDR);
75 return ok;
76}
77
78/* Quick test to see if A20 is already enabled */
79static int a20_test_short(void)
80{
81 return a20_test(A20_TEST_SHORT);
82}
83
84/* Longer test that actually waits for A20 to come on line; this
85 is useful when dealing with the KBC or other slow external circuitry. */
86static int a20_test_long(void)
87{
88 return a20_test(A20_TEST_LONG);
89}
90
91static void enable_a20_bios(void)
92{
93 asm volatile("pushfl; int $0x15; popfl"
94 : : "a" ((u16)0x2401));
95}
96
97static void enable_a20_kbc(void)
98{
99 empty_8042();
100
101 outb(0xd1, 0x64); /* Command write */
102 empty_8042();
103
104 outb(0xdf, 0x60); /* A20 on */
105 empty_8042();
H. Peter Anvinaa60d132008-06-27 13:23:00 -0700106
107 outb(0xff, 0x64); /* Null command, but UHCI wants it */
108 empty_8042();
H. Peter Anvin5a8a8122007-07-11 12:18:42 -0700109}
110
111static void enable_a20_fast(void)
112{
113 u8 port_a;
114
115 port_a = inb(0x92); /* Configuration port A */
116 port_a |= 0x02; /* Enable A20 */
117 port_a &= ~0x01; /* Do not reset machine */
118 outb(port_a, 0x92);
119}
120
121/*
122 * Actual routine to enable A20; return 0 on ok, -1 on failure
123 */
124
125#define A20_ENABLE_LOOPS 255 /* Number of times to try */
126
127int enable_a20(void)
128{
H. Peter Anvin3bd323a2009-02-02 14:52:00 -0800129#ifdef CONFIG_X86_VOYAGER
H. Peter Anvin5a8a8122007-07-11 12:18:42 -0700130 /* On Voyager, a20_test() is unsafe? */
131 enable_a20_kbc();
132 return 0;
133#else
Manish Katiyar52aaa122008-06-05 19:14:15 +0530134 int loops = A20_ENABLE_LOOPS;
H. Peter Anvin3bd323a2009-02-02 14:52:00 -0800135 int kbc_err;
H. Peter Anvin5a8a8122007-07-11 12:18:42 -0700136
H. Peter Anvin3bd323a2009-02-02 14:52:00 -0800137 while (loops--) {
138 /* First, check to see if A20 is already enabled
139 (legacy free, etc.) */
140 if (a20_test_short())
141 return 0;
142
143 /* Next, try the BIOS (INT 0x15, AX=0x2401) */
144 enable_a20_bios();
145 if (a20_test_short())
146 return 0;
147
148 /* Try enabling A20 through the keyboard controller */
149 kbc_err = empty_8042();
H. Peter Anvin5a8a8122007-07-11 12:18:42 -0700150
H. Peter Anvin3bd323a2009-02-02 14:52:00 -0800151 if (a20_test_short())
152 return 0; /* BIOS worked, but with delayed reaction */
153
154 if (!kbc_err) {
155 enable_a20_kbc();
156 if (a20_test_long())
157 return 0;
158 }
159
160 /* Finally, try enabling the "fast A20 gate" */
161 enable_a20_fast();
162 if (a20_test_long())
163 return 0;
164 }
165
166 return -1;
H. Peter Anvin5a8a8122007-07-11 12:18:42 -0700167#endif
168}