#include <linux/linkage.h>
#include <linux/init.h>
#include <asm/segment.h>
#include <asm/page_types.h>
/*
* The following code and data reboots the machine by switching to real
* mode and jumping to the BIOS reset entry point, as if the CPU has
* really been reset. The previous version asked the keyboard
* controller to pulse the CPU reset line, which is more thorough, but
* doesn't work with at least one type of 486 motherboard. It is easy
* to stop this code working; hence the copious comments.
*
* This code is called with the restart type (0 = BIOS, 1 = APM) in %eax.
*/
.section ".x86_trampoline","a"
.balign 16
.code32
ENTRY(machine_real_restart_asm)
r_base = .
/* Get our own relocated address */
call 1f
1: popl %ebx
subl $(1b - r_base), %ebx
/* Compute the equivalent real-mode segment */
movl %ebx, %ecx
shrl $4, %ecx
/* Patch post-real-mode segment jump */
movw (dispatch_table - r_base)(%ebx,%eax,2),%ax
movw %ax, (101f - r_base)(%ebx)
movw %cx, (102f - r_base)(%ebx)
/* Set up the IDT for real mode. */
lidtl (machine_real_restart_idt - r_base)(%ebx)
/*
* Set up a GDT from which we can load segment descriptors for real
* mode. The GDT is not used in real mode; it is just needed here to
* prepare the descriptors.
*/
lgdtl (machine_real_restart_gdt - r_base)(%ebx)
/*
* Load the data segment registers with 16-bit compatible values
*/
movl $16, %ecx
movl %ecx, %ds
movl %ecx, %es
movl %ecx, %fs
movl %ecx, %gs
movl %ecx, %ss
ljmpl $8, $1f - r_base
/*
* This is 16-bit protected mode code to disable paging and the cache,
* switch to real mode and jump to the BIOS reset code.
*
* The instruction that switches to real mode by writing to CR0 must be
* followed immediately by a far jump instruction, which set CS to a
* valid value for real mode, and flushes the prefetch queue to avoid
* running instructions that have already been decoded in protected
* mode.
*
* Clears all the flags except ET, especially PG (paging), PE
* (protected-mode enable) and TS (task switch for coprocessor state
* save). Flushes the TLB after paging has been disabled. Sets CD and
* NW, to disable the cache on a 486, and invalidates the cache. This
* is more like the state of a 486 after reset. I don't know if
* something else should be done for other chips.
*
* More could be done here to set up the registers as if a CPU reset had
* occurred; hopefully real BIOSs don't assume much. This is not the
* actual BIOS entry point, anyway (that is at 0xfffffff0).
*
* Most of this work is probably excessive, but it is what is tested.
*/
.code16
1:
xorl %ecx, %ecx
movl %cr0, %eax
andl $0x00000011, %eax
orl $0x60000000, %eax
movl %eax, %cr0
movl %ecx, %cr3
movl %cr0, %edx
andl $0x60000000, %edx /* If no cache bits -> no wbinvd */
jz 2f
wbinvd
2:
andb $0x10, %al
movl %eax, %cr0
.byte 0xea /* ljmpw */
101: .word 0 /* Offset */
102: .word 0 /* Segment */
bios:
ljmpw $0xf000, $0xfff0
apm:
movw $0x1000, %ax
movw %ax, %ss
movw $0xf000, %sp
movw $0x5307, %ax
movw $0x0001, %bx
movw $0x0003, %cx
int $0x15
END(machine_real_restart_asm)
.balign 16
/* These must match <asm/reboot.h */
dispatch_table:
.word bios - r_base
.word apm - r_base
END(dispatch_table)
.balign 16
machine_real_restart_idt:
.word 0xffff /* Length - real mode default value */
.long 0 /* Base - real mode default value */
END(machine_real_restart_idt)
.balign 16
ENTRY(machine_real_restart_gdt)
.quad 0 /* Self-pointer, filled in by PM code */
.quad 0 /* 16-bit code segment, filled in by PM code */
/*
* 16-bit data segment with the selector value 16 = 0x10 and
* base value 0x100; since this is consistent with real mode
* semantics we don't have to reload the segments once CR0.PE = 0.
*/
.quad GDT_ENTRY(0x0093, 0x100, 0xffff)
END(machine_real_restart_gdt)
