--- /dev/null
+/*
+ * Copyright (C) 2010 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER )
+
+ .arch i386
+
+/****************************************************************************
+ * test_a20_short, test_a20_long
+ *
+ * Check to see if A20 line is enabled
+ *
+ * Parameters:
+ * none
+ * Returns:
+ * CF set if A20 line is not enabled
+ * Corrupts:
+ * none
+ ****************************************************************************
+ */
+#define TEST_A20_SHORT_MAX_RETRIES 0x20
+#define TEST_A20_LONG_MAX_RETRIES 0x200000
+ .section ".text16.early", "awx", @progbits
+ .code16
+test_a20_short:
+ pushl %ecx
+ movl $TEST_A20_SHORT_MAX_RETRIES, %ecx
+ jmp 1f
+ .size test_a20_short, . - test_a20_short
+test_a20_long:
+ pushl %ecx
+ movl $TEST_A20_LONG_MAX_RETRIES, %ecx
+1: pushw %ax
+ pushw %ds
+ pushw %es
+
+ /* Set up segment registers for access across the 1MB boundary */
+ xorw %ax, %ax
+ movw %ax, %ds
+ decw %ax
+ movw %ax, %es
+
+2: /* Modify and check test pattern; succeed if we see a difference */
+ pushfw
+ cli
+ xchgw %ds:0, %cx
+ movw %es:0x10, %ax
+ xchgw %ds:0, %cx
+ popfw
+ cmpw %ax, %cx
+ clc
+ jnz 99f
+
+ /* Delay and retry */
+ outb %al, $0x80
+ addr32 loop 2b
+ stc
+
+99: /* Restore registers and return */
+ popw %es
+ popw %ds
+ popw %ax
+ popl %ecx
+ ret
+ .size test_a20_long, . - test_a20_long
+
+/****************************************************************************
+ * enable_a20_bios
+ *
+ * Try enabling A20 line via BIOS
+ *
+ * Parameters:
+ * none
+ * Returns:
+ * CF set if A20 line is not enabled
+ * Corrupts:
+ * none
+ ****************************************************************************
+ */
+ .section ".text16.early", "awx", @progbits
+ .code16
+enable_a20_bios:
+
+ /* Preserve registers. Be very paranoid, since some BIOSes
+ * are reported to clobber %ebx
+ */
+ pushal
+
+ /* Attempt INT 15,2401 */
+ movw $0x2401, %ax
+ int $0x15
+ jc 99f
+
+ /* Check that success was really successful */
+ call test_a20_short
+
+99: /* Restore registers and return */
+ popal
+ ret
+ .size enable_a20_bios, . - enable_a20_bios
+
+/****************************************************************************
+ * enable_a20_kbc
+ *
+ * Try enabling A20 line via keyboard controller
+ *
+ * Parameters:
+ * none
+ * Returns:
+ * CF set if A20 line is not enabled
+ * Corrupts:
+ * none
+ ****************************************************************************
+ */
+#define KC_RDWR 0x60
+#define KC_RDWR_SET_A20 0xdf
+#define KC_CMD 0x64
+#define KC_CMD_WOUT 0xd1
+#define KC_CMD_NULL 0xff
+#define KC_STATUS 0x64
+#define KC_STATUS_OBUF_FULL 0x01
+#define KC_STATUS_IBUF_FULL 0x02
+#define KC_MAX_RETRIES 100000
+ .section ".text16.early", "awx", @progbits
+ .code16
+enable_a20_kbc:
+ /* Preserve registers */
+ pushw %ax
+
+ /* Try keyboard controller */
+ call empty_kbc
+ movb $KC_CMD_WOUT, %al
+ outb %al, $KC_CMD
+ call empty_kbc
+ movb $KC_RDWR_SET_A20, %al
+ outb %al, $KC_RDWR
+ call empty_kbc
+ movb $KC_CMD_NULL, %al
+ outb %al, $KC_CMD
+ call empty_kbc
+
+ /* Check to see if it worked */
+ call test_a20_long
+
+ /* Restore registers and return */
+ popw %ax
+ ret
+ .size enable_a20_kbc, . - enable_a20_kbc
+
+ .section ".text16.early", "awx", @progbits
+ .code16
+empty_kbc:
+ /* Preserve registers */
+ pushl %ecx
+ pushw %ax
+
+ /* Wait for KBC to become empty */
+ movl $KC_MAX_RETRIES, %ecx
+1: outb %al, $0x80
+ inb $KC_STATUS, %al
+ testb $( KC_STATUS_OBUF_FULL | KC_STATUS_IBUF_FULL ), %al
+ jz 99f
+ testb $KC_STATUS_OBUF_FULL, %al
+ jz 2f
+ outb %al, $0x80
+ inb $KC_RDWR, %al
+2: addr32 loop 1b
+
+99: /* Restore registers and return */
+ popw %ax
+ popl %ecx
+ ret
+ .size empty_kbc, . - empty_kbc
+
+/****************************************************************************
+ * enable_a20_fast
+ *
+ * Try enabling A20 line via "Fast Gate A20"
+ *
+ * Parameters:
+ * none
+ * Returns:
+ * CF set if A20 line is not enabled
+ * Corrupts:
+ * none
+ ****************************************************************************
+ */
+#define SCP_A 0x92
+ .section ".text16.early", "awx", @progbits
+ .code16
+enable_a20_fast:
+ /* Preserve registers */
+ pushw %ax
+
+ /* Try "Fast Gate A20" */
+ inb $SCP_A, %al
+ orb $0x02, %al
+ andb $~0x01, %al
+ outb %al, $SCP_A
+
+ /* Check to see if it worked */
+ call test_a20_long
+
+ /* Restore registers and return */
+ popw %ax
+ ret
+ .size enable_a20_fast, . - enable_a20_fast
+
+/****************************************************************************
+ * enable_a20
+ *
+ * Try enabling A20 line via any available method
+ *
+ * Parameters:
+ * none
+ * Returns:
+ * CF set if A20 line is not enabled
+ * Corrupts:
+ * none
+ ****************************************************************************
+ */
+#define ENABLE_A20_RETRIES 255
+ .section ".text16.early", "awx", @progbits
+ .code16
+ .globl enable_a20
+enable_a20:
+ /* Preserve registers */
+ pushl %ecx
+ pushw %ax
+
+ /* Check to see if A20 is already enabled */
+ call test_a20_short
+ jnc 99f
+
+ /* Use known working method, if we have one */
+ movw %cs:enable_a20_method, %ax
+ testw %ax, %ax
+ jz 1f
+ call *%ax
+ jmp 99f
+1:
+ /* Try all methods in turn until one works */
+ movl $ENABLE_A20_RETRIES, %ecx
+2: movw $enable_a20_bios, %ax
+ movw %ax, %cs:enable_a20_method
+ call *%ax
+ jnc 99f
+ movw $enable_a20_kbc, %ax
+ movw %ax, %cs:enable_a20_method
+ call *%ax
+ jnc 99f
+ movw $enable_a20_fast, %ax
+ movw %ax, %cs:enable_a20_method
+ call *%ax
+ jnc 99f
+ addr32 loop 2b
+ /* Failure; exit with carry set */
+ movw $0, %cs:enable_a20_method
+ stc
+
+99: /* Restore registers and return */
+ popw %ax
+ popl %ecx
+ ret
+
+ .section ".text16.early.data", "aw", @progbits
+ .align 2
+enable_a20_method:
+ .word 0
+ .size enable_a20_method, . - enable_a20_method
+
+/****************************************************************************
+ * access_highmem (real mode far call)
+ *
+ * Open up access to high memory with A20 enabled
+ *
+ * Parameters:
+ * none
+ * Returns:
+ * CF set if high memory could not be accessed
+ * Corrupts:
+ * none
+ ****************************************************************************
+ */
+ .section ".text16.early", "awx", @progbits
+ .code16
+ .globl access_highmem
+access_highmem:
+ /* Enable A20 line */
+ call enable_a20
+ lret
+ .size access_highmem, . - access_highmem
Code Review / kvmfornfv.git / blobdiff