166 lines
3.5 KiB
C
Executable File
166 lines
3.5 KiB
C
Executable File
/* -*- linux-c -*- ------------------------------------------------------- *
|
|
*
|
|
* Copyright (C) 1991, 1992 Linus Torvalds
|
|
* Copyright 2007-2008 rPath, Inc. - All Rights Reserved
|
|
* Copyright 2009 Intel Corporation; author H. Peter Anvin
|
|
*
|
|
* This file is part of the Linux kernel, and is made available under
|
|
* the terms of the GNU General Public License version 2.
|
|
*
|
|
* ----------------------------------------------------------------------- */
|
|
|
|
/*
|
|
* Enable A20 gate (return -1 on failure)
|
|
*/
|
|
|
|
#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();
|
|
(void)inb(0x60);
|
|
} else if (!(status & 2)) {
|
|
/* Buffers empty, finished! */
|
|
return 0;
|
|
}
|
|
}
|
|
|
|
return -1;
|
|
}
|
|
|
|
/* Returns nonzero if the A20 line is enabled. The memory address
|
|
used as a test is the int $0x80 vector, which should be safe. */
|
|
|
|
#define A20_TEST_ADDR (4*0x80)
|
|
#define A20_TEST_SHORT 32
|
|
#define A20_TEST_LONG 2097152 /* 2^21 */
|
|
|
|
static int a20_test(int loops)
|
|
{
|
|
int ok = 0;
|
|
int saved, ctr;
|
|
|
|
set_fs(0x0000);
|
|
set_gs(0xffff);
|
|
|
|
saved = ctr = rdfs32(A20_TEST_ADDR);
|
|
|
|
while (loops--) {
|
|
wrfs32(++ctr, A20_TEST_ADDR);
|
|
io_delay(); /* Serialize and make delay constant */
|
|
ok = rdgs32(A20_TEST_ADDR+0x10) ^ ctr;
|
|
if (ok)
|
|
break;
|
|
}
|
|
|
|
wrfs32(saved, A20_TEST_ADDR);
|
|
return ok;
|
|
}
|
|
|
|
/* Quick test to see if A20 is already enabled */
|
|
static int a20_test_short(void)
|
|
{
|
|
return a20_test(A20_TEST_SHORT);
|
|
}
|
|
|
|
/* Longer test that actually waits for A20 to come on line; this
|
|
is useful when dealing with the KBC or other slow external circuitry. */
|
|
static int a20_test_long(void)
|
|
{
|
|
return a20_test(A20_TEST_LONG);
|
|
}
|
|
|
|
static void enable_a20_bios(void)
|
|
{
|
|
struct biosregs ireg;
|
|
|
|
initregs(&ireg);
|
|
ireg.ax = 0x2401;
|
|
intcall(0x15, &ireg, NULL);
|
|
}
|
|
|
|
static void enable_a20_kbc(void)
|
|
{
|
|
empty_8042();
|
|
|
|
outb(0xd1, 0x64); /* Command write */
|
|
empty_8042();
|
|
|
|
outb(0xdf, 0x60); /* A20 on */
|
|
empty_8042();
|
|
|
|
outb(0xff, 0x64); /* Null command, but UHCI wants it */
|
|
empty_8042();
|
|
}
|
|
|
|
static void enable_a20_fast(void)
|
|
{
|
|
u8 port_a;
|
|
|
|
port_a = inb(0x92); /* Configuration port A */
|
|
port_a |= 0x02; /* Enable A20 */
|
|
port_a &= ~0x01; /* Do not reset machine */
|
|
outb(port_a, 0x92);
|
|
}
|
|
|
|
/*
|
|
* Actual routine to enable A20; return 0 on ok, -1 on failure
|
|
*/
|
|
|
|
#define A20_ENABLE_LOOPS 255 /* Number of times to try */
|
|
|
|
int enable_a20(void)
|
|
{
|
|
int loops = A20_ENABLE_LOOPS;
|
|
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;
|
|
}
|