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5a8a8128 PA |
1 | /* -*- linux-c -*- ------------------------------------------------------- * |
2 | * | |
3 | * Copyright (C) 1991, 1992 Linus Torvalds | |
4 | * Copyright 2007 rPath, Inc. - All Rights Reserved | |
5 | * | |
6 | * This file is part of the Linux kernel, and is made available under | |
7 | * the terms of the GNU General Public License version 2. | |
8 | * | |
9 | * ----------------------------------------------------------------------- */ | |
10 | ||
11 | /* | |
12 | * arch/i386/boot/a20.c | |
13 | * | |
14 | * Enable A20 gate (return -1 on failure) | |
15 | */ | |
16 | ||
17 | #include "boot.h" | |
18 | ||
19 | #define MAX_8042_LOOPS 100000 | |
20 | ||
21 | static int empty_8042(void) | |
22 | { | |
23 | u8 status; | |
24 | int loops = MAX_8042_LOOPS; | |
25 | ||
26 | while (loops--) { | |
27 | io_delay(); | |
28 | ||
29 | status = inb(0x64); | |
30 | if (status & 1) { | |
31 | /* Read and discard input data */ | |
32 | io_delay(); | |
33 | (void)inb(0x60); | |
34 | } else if (!(status & 2)) { | |
35 | /* Buffers empty, finished! */ | |
36 | return 0; | |
37 | } | |
38 | } | |
39 | ||
40 | return -1; | |
41 | } | |
42 | ||
43 | /* Returns nonzero if the A20 line is enabled. The memory address | |
44 | used as a test is the int $0x80 vector, which should be safe. */ | |
45 | ||
46 | #define A20_TEST_ADDR (4*0x80) | |
47 | #define A20_TEST_SHORT 32 | |
48 | #define A20_TEST_LONG 2097152 /* 2^21 */ | |
49 | ||
50 | static int a20_test(int loops) | |
51 | { | |
52 | int ok = 0; | |
53 | int saved, ctr; | |
54 | ||
55 | set_fs(0x0000); | |
56 | set_gs(0xffff); | |
57 | ||
58 | saved = ctr = rdfs32(A20_TEST_ADDR); | |
59 | ||
60 | while (loops--) { | |
61 | wrfs32(++ctr, A20_TEST_ADDR); | |
62 | io_delay(); /* Serialize and make delay constant */ | |
63 | ok = rdgs32(A20_TEST_ADDR+0x10) ^ ctr; | |
64 | if (ok) | |
65 | break; | |
66 | } | |
67 | ||
68 | wrfs32(saved, A20_TEST_ADDR); | |
69 | return ok; | |
70 | } | |
71 | ||
72 | /* Quick test to see if A20 is already enabled */ | |
73 | static int a20_test_short(void) | |
74 | { | |
75 | return a20_test(A20_TEST_SHORT); | |
76 | } | |
77 | ||
78 | /* Longer test that actually waits for A20 to come on line; this | |
79 | is useful when dealing with the KBC or other slow external circuitry. */ | |
80 | static int a20_test_long(void) | |
81 | { | |
82 | return a20_test(A20_TEST_LONG); | |
83 | } | |
84 | ||
85 | static void enable_a20_bios(void) | |
86 | { | |
87 | asm volatile("pushfl; int $0x15; popfl" | |
88 | : : "a" ((u16)0x2401)); | |
89 | } | |
90 | ||
91 | static void enable_a20_kbc(void) | |
92 | { | |
93 | empty_8042(); | |
94 | ||
95 | outb(0xd1, 0x64); /* Command write */ | |
96 | empty_8042(); | |
97 | ||
98 | outb(0xdf, 0x60); /* A20 on */ | |
99 | empty_8042(); | |
100 | } | |
101 | ||
102 | static void enable_a20_fast(void) | |
103 | { | |
104 | u8 port_a; | |
105 | ||
106 | port_a = inb(0x92); /* Configuration port A */ | |
107 | port_a |= 0x02; /* Enable A20 */ | |
108 | port_a &= ~0x01; /* Do not reset machine */ | |
109 | outb(port_a, 0x92); | |
110 | } | |
111 | ||
112 | /* | |
113 | * Actual routine to enable A20; return 0 on ok, -1 on failure | |
114 | */ | |
115 | ||
116 | #define A20_ENABLE_LOOPS 255 /* Number of times to try */ | |
117 | ||
118 | int enable_a20(void) | |
119 | { | |
120 | int loops = A20_ENABLE_LOOPS; | |
121 | ||
122 | #if defined(CONFIG_X86_ELAN) | |
123 | /* Elan croaks if we try to touch the KBC */ | |
124 | enable_a20_fast(); | |
125 | while (!a20_test_long()) | |
126 | ; | |
127 | return 0; | |
128 | #elif defined(CONFIG_X86_VOYAGER) | |
129 | /* On Voyager, a20_test() is unsafe? */ | |
130 | enable_a20_kbc(); | |
131 | return 0; | |
132 | #else | |
133 | while (loops--) { | |
134 | /* First, check to see if A20 is already enabled | |
135 | (legacy free, etc.) */ | |
136 | if (a20_test_short()) | |
137 | return 0; | |
138 | ||
139 | /* Next, try the BIOS (INT 0x15, AX=0x2401) */ | |
140 | enable_a20_bios(); | |
141 | if (a20_test_short()) | |
142 | return 0; | |
143 | ||
144 | /* Try enabling A20 through the keyboard controller */ | |
145 | empty_8042(); | |
146 | if (a20_test_short()) | |
147 | return 0; /* BIOS worked, but with delayed reaction */ | |
148 | ||
149 | enable_a20_kbc(); | |
150 | if (a20_test_long()) | |
151 | return 0; | |
152 | ||
153 | /* Finally, try enabling the "fast A20 gate" */ | |
154 | enable_a20_fast(); | |
155 | if (a20_test_long()) | |
156 | return 0; | |
157 | } | |
158 | ||
159 | return -1; | |
160 | #endif | |
161 | } |