1*4882a593Smuzhiyun // SPDX-License-Identifier: GPL-2.0-only
2*4882a593Smuzhiyun /* -*- linux-c -*- ------------------------------------------------------- *
3*4882a593Smuzhiyun *
4*4882a593Smuzhiyun * Copyright (C) 1991, 1992 Linus Torvalds
5*4882a593Smuzhiyun * Copyright 2007-2008 rPath, Inc. - All Rights Reserved
6*4882a593Smuzhiyun * Copyright 2009 Intel Corporation; author H. Peter Anvin
7*4882a593Smuzhiyun *
8*4882a593Smuzhiyun * ----------------------------------------------------------------------- */
9*4882a593Smuzhiyun
10*4882a593Smuzhiyun /*
11*4882a593Smuzhiyun * Enable A20 gate (return -1 on failure)
12*4882a593Smuzhiyun */
13*4882a593Smuzhiyun
14*4882a593Smuzhiyun #include "boot.h"
15*4882a593Smuzhiyun
16*4882a593Smuzhiyun #define MAX_8042_LOOPS 100000
17*4882a593Smuzhiyun #define MAX_8042_FF 32
18*4882a593Smuzhiyun
empty_8042(void)19*4882a593Smuzhiyun static int empty_8042(void)
20*4882a593Smuzhiyun {
21*4882a593Smuzhiyun u8 status;
22*4882a593Smuzhiyun int loops = MAX_8042_LOOPS;
23*4882a593Smuzhiyun int ffs = MAX_8042_FF;
24*4882a593Smuzhiyun
25*4882a593Smuzhiyun while (loops--) {
26*4882a593Smuzhiyun io_delay();
27*4882a593Smuzhiyun
28*4882a593Smuzhiyun status = inb(0x64);
29*4882a593Smuzhiyun if (status == 0xff) {
30*4882a593Smuzhiyun /* FF is a plausible, but very unlikely status */
31*4882a593Smuzhiyun if (!--ffs)
32*4882a593Smuzhiyun return -1; /* Assume no KBC present */
33*4882a593Smuzhiyun }
34*4882a593Smuzhiyun if (status & 1) {
35*4882a593Smuzhiyun /* Read and discard input data */
36*4882a593Smuzhiyun io_delay();
37*4882a593Smuzhiyun (void)inb(0x60);
38*4882a593Smuzhiyun } else if (!(status & 2)) {
39*4882a593Smuzhiyun /* Buffers empty, finished! */
40*4882a593Smuzhiyun return 0;
41*4882a593Smuzhiyun }
42*4882a593Smuzhiyun }
43*4882a593Smuzhiyun
44*4882a593Smuzhiyun return -1;
45*4882a593Smuzhiyun }
46*4882a593Smuzhiyun
47*4882a593Smuzhiyun /* Returns nonzero if the A20 line is enabled. The memory address
48*4882a593Smuzhiyun used as a test is the int $0x80 vector, which should be safe. */
49*4882a593Smuzhiyun
50*4882a593Smuzhiyun #define A20_TEST_ADDR (4*0x80)
51*4882a593Smuzhiyun #define A20_TEST_SHORT 32
52*4882a593Smuzhiyun #define A20_TEST_LONG 2097152 /* 2^21 */
53*4882a593Smuzhiyun
a20_test(int loops)54*4882a593Smuzhiyun static int a20_test(int loops)
55*4882a593Smuzhiyun {
56*4882a593Smuzhiyun int ok = 0;
57*4882a593Smuzhiyun int saved, ctr;
58*4882a593Smuzhiyun
59*4882a593Smuzhiyun set_fs(0x0000);
60*4882a593Smuzhiyun set_gs(0xffff);
61*4882a593Smuzhiyun
62*4882a593Smuzhiyun saved = ctr = rdfs32(A20_TEST_ADDR);
63*4882a593Smuzhiyun
64*4882a593Smuzhiyun while (loops--) {
65*4882a593Smuzhiyun wrfs32(++ctr, A20_TEST_ADDR);
66*4882a593Smuzhiyun io_delay(); /* Serialize and make delay constant */
67*4882a593Smuzhiyun ok = rdgs32(A20_TEST_ADDR+0x10) ^ ctr;
68*4882a593Smuzhiyun if (ok)
69*4882a593Smuzhiyun break;
70*4882a593Smuzhiyun }
71*4882a593Smuzhiyun
72*4882a593Smuzhiyun wrfs32(saved, A20_TEST_ADDR);
73*4882a593Smuzhiyun return ok;
74*4882a593Smuzhiyun }
75*4882a593Smuzhiyun
76*4882a593Smuzhiyun /* Quick test to see if A20 is already enabled */
a20_test_short(void)77*4882a593Smuzhiyun static int a20_test_short(void)
78*4882a593Smuzhiyun {
79*4882a593Smuzhiyun return a20_test(A20_TEST_SHORT);
80*4882a593Smuzhiyun }
81*4882a593Smuzhiyun
82*4882a593Smuzhiyun /* Longer test that actually waits for A20 to come on line; this
83*4882a593Smuzhiyun is useful when dealing with the KBC or other slow external circuitry. */
a20_test_long(void)84*4882a593Smuzhiyun static int a20_test_long(void)
85*4882a593Smuzhiyun {
86*4882a593Smuzhiyun return a20_test(A20_TEST_LONG);
87*4882a593Smuzhiyun }
88*4882a593Smuzhiyun
enable_a20_bios(void)89*4882a593Smuzhiyun static void enable_a20_bios(void)
90*4882a593Smuzhiyun {
91*4882a593Smuzhiyun struct biosregs ireg;
92*4882a593Smuzhiyun
93*4882a593Smuzhiyun initregs(&ireg);
94*4882a593Smuzhiyun ireg.ax = 0x2401;
95*4882a593Smuzhiyun intcall(0x15, &ireg, NULL);
96*4882a593Smuzhiyun }
97*4882a593Smuzhiyun
enable_a20_kbc(void)98*4882a593Smuzhiyun static void enable_a20_kbc(void)
99*4882a593Smuzhiyun {
100*4882a593Smuzhiyun empty_8042();
101*4882a593Smuzhiyun
102*4882a593Smuzhiyun outb(0xd1, 0x64); /* Command write */
103*4882a593Smuzhiyun empty_8042();
104*4882a593Smuzhiyun
105*4882a593Smuzhiyun outb(0xdf, 0x60); /* A20 on */
106*4882a593Smuzhiyun empty_8042();
107*4882a593Smuzhiyun
108*4882a593Smuzhiyun outb(0xff, 0x64); /* Null command, but UHCI wants it */
109*4882a593Smuzhiyun empty_8042();
110*4882a593Smuzhiyun }
111*4882a593Smuzhiyun
enable_a20_fast(void)112*4882a593Smuzhiyun static void enable_a20_fast(void)
113*4882a593Smuzhiyun {
114*4882a593Smuzhiyun u8 port_a;
115*4882a593Smuzhiyun
116*4882a593Smuzhiyun port_a = inb(0x92); /* Configuration port A */
117*4882a593Smuzhiyun port_a |= 0x02; /* Enable A20 */
118*4882a593Smuzhiyun port_a &= ~0x01; /* Do not reset machine */
119*4882a593Smuzhiyun outb(port_a, 0x92);
120*4882a593Smuzhiyun }
121*4882a593Smuzhiyun
122*4882a593Smuzhiyun /*
123*4882a593Smuzhiyun * Actual routine to enable A20; return 0 on ok, -1 on failure
124*4882a593Smuzhiyun */
125*4882a593Smuzhiyun
126*4882a593Smuzhiyun #define A20_ENABLE_LOOPS 255 /* Number of times to try */
127*4882a593Smuzhiyun
enable_a20(void)128*4882a593Smuzhiyun int enable_a20(void)
129*4882a593Smuzhiyun {
130*4882a593Smuzhiyun int loops = A20_ENABLE_LOOPS;
131*4882a593Smuzhiyun int kbc_err;
132*4882a593Smuzhiyun
133*4882a593Smuzhiyun while (loops--) {
134*4882a593Smuzhiyun /* First, check to see if A20 is already enabled
135*4882a593Smuzhiyun (legacy free, etc.) */
136*4882a593Smuzhiyun if (a20_test_short())
137*4882a593Smuzhiyun return 0;
138*4882a593Smuzhiyun
139*4882a593Smuzhiyun /* Next, try the BIOS (INT 0x15, AX=0x2401) */
140*4882a593Smuzhiyun enable_a20_bios();
141*4882a593Smuzhiyun if (a20_test_short())
142*4882a593Smuzhiyun return 0;
143*4882a593Smuzhiyun
144*4882a593Smuzhiyun /* Try enabling A20 through the keyboard controller */
145*4882a593Smuzhiyun kbc_err = empty_8042();
146*4882a593Smuzhiyun
147*4882a593Smuzhiyun if (a20_test_short())
148*4882a593Smuzhiyun return 0; /* BIOS worked, but with delayed reaction */
149*4882a593Smuzhiyun
150*4882a593Smuzhiyun if (!kbc_err) {
151*4882a593Smuzhiyun enable_a20_kbc();
152*4882a593Smuzhiyun if (a20_test_long())
153*4882a593Smuzhiyun return 0;
154*4882a593Smuzhiyun }
155*4882a593Smuzhiyun
156*4882a593Smuzhiyun /* Finally, try enabling the "fast A20 gate" */
157*4882a593Smuzhiyun enable_a20_fast();
158*4882a593Smuzhiyun if (a20_test_long())
159*4882a593Smuzhiyun return 0;
160*4882a593Smuzhiyun }
161*4882a593Smuzhiyun
162*4882a593Smuzhiyun return -1;
163*4882a593Smuzhiyun }
164