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1 | /* -*- linux-c -*- ------------------------------------------------------- * |
2 | * | |
3 | * Copyright (C) 1991, 1992 Linus Torvalds | |
aa60d13f | 4 | * Copyright 2007-2008 rPath, Inc. - All Rights Reserved |
df7699c5 | 5 | * Copyright 2009 Intel Corporation; author H. Peter Anvin |
5a8a8128 PA |
6 | * |
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 | /* | |
5a8a8128 PA |
13 | * Enable A20 gate (return -1 on failure) |
14 | */ | |
15 | ||
16 | #include "boot.h" | |
17 | ||
18 | #define MAX_8042_LOOPS 100000 | |
3bd323a1 | 19 | #define MAX_8042_FF 32 |
5a8a8128 PA |
20 | |
21 | static int empty_8042(void) | |
22 | { | |
23 | u8 status; | |
24 | int loops = MAX_8042_LOOPS; | |
3bd323a1 | 25 | int ffs = MAX_8042_FF; |
5a8a8128 PA |
26 | |
27 | while (loops--) { | |
28 | io_delay(); | |
29 | ||
30 | status = inb(0x64); | |
3bd323a1 PA |
31 | if (status == 0xff) { |
32 | /* FF is a plausible, but very unlikely status */ | |
33 | if (!--ffs) | |
34 | return -1; /* Assume no KBC present */ | |
35 | } | |
5a8a8128 PA |
36 | 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 | ||
56 | static 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 */ | |
79 | static 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. */ | |
86 | static int a20_test_long(void) | |
87 | { | |
88 | return a20_test(A20_TEST_LONG); | |
89 | } | |
90 | ||
91 | static void enable_a20_bios(void) | |
92 | { | |
df7699c5 PA |
93 | struct biosregs ireg; |
94 | ||
95 | initregs(&ireg); | |
96 | ireg.ax = 0x2401; | |
97 | intcall(0x15, &ireg, NULL); | |
5a8a8128 PA |
98 | } |
99 | ||
100 | static void enable_a20_kbc(void) | |
101 | { | |
102 | empty_8042(); | |
103 | ||
104 | outb(0xd1, 0x64); /* Command write */ | |
105 | empty_8042(); | |
106 | ||
107 | outb(0xdf, 0x60); /* A20 on */ | |
108 | empty_8042(); | |
aa60d13f PA |
109 | |
110 | outb(0xff, 0x64); /* Null command, but UHCI wants it */ | |
111 | empty_8042(); | |
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112 | } |
113 | ||
114 | static void enable_a20_fast(void) | |
115 | { | |
116 | u8 port_a; | |
117 | ||
118 | port_a = inb(0x92); /* Configuration port A */ | |
119 | port_a |= 0x02; /* Enable A20 */ | |
120 | port_a &= ~0x01; /* Do not reset machine */ | |
121 | outb(port_a, 0x92); | |
122 | } | |
123 | ||
124 | /* | |
125 | * Actual routine to enable A20; return 0 on ok, -1 on failure | |
126 | */ | |
127 | ||
128 | #define A20_ENABLE_LOOPS 255 /* Number of times to try */ | |
129 | ||
130 | int enable_a20(void) | |
131 | { | |
52aaa12f | 132 | int loops = A20_ENABLE_LOOPS; |
3bd323a1 PA |
133 | int kbc_err; |
134 | ||
135 | while (loops--) { | |
136 | /* First, check to see if A20 is already enabled | |
137 | (legacy free, etc.) */ | |
138 | if (a20_test_short()) | |
139 | return 0; | |
140 | ||
141 | /* Next, try the BIOS (INT 0x15, AX=0x2401) */ | |
142 | enable_a20_bios(); | |
143 | if (a20_test_short()) | |
144 | return 0; | |
145 | ||
146 | /* Try enabling A20 through the keyboard controller */ | |
147 | kbc_err = empty_8042(); | |
148 | ||
149 | if (a20_test_short()) | |
150 | return 0; /* BIOS worked, but with delayed reaction */ | |
151 | ||
152 | if (!kbc_err) { | |
153 | enable_a20_kbc(); | |
154 | if (a20_test_long()) | |
155 | return 0; | |
156 | } | |
157 | ||
158 | /* Finally, try enabling the "fast A20 gate" */ | |
159 | enable_a20_fast(); | |
160 | if (a20_test_long()) | |
161 | return 0; | |
162 | } | |
163 | ||
164 | return -1; | |
5a8a8128 | 165 | } |