1 /* SPDX-License-Identifier: GPL-2.0 */
2 #include <linux/linkage.h>
3 #include <asm/desc_defs.h>
4 #include <asm/segment.h>
5 #include <asm/page_types.h>
6 #include <asm/processor-flags.h>
7 #include <asm/msr-index.h>
8 #include "realmode.h"
9
10 /*
11 * The following code and data reboots the mac
12 * mode and jumping to the BIOS reset entry po
13 * really been reset. The previous version as
14 * controller to pulse the CPU reset line, whi
15 * doesn't work with at least one type of 486
16 * to stop this code working; hence the copiou
17 *
18 * This code is called with the restart type (
19 * the primary argument register (%eax for 32
20 */
21 .section ".text32", "ax"
22 .code32
23 SYM_CODE_START(machine_real_restart_asm)
24
25 #ifdef CONFIG_X86_64
26 /* Switch to trampoline GDT as it is g
27 movl $__KERNEL_DS, %eax
28 movl %eax, %ds
29 lgdtl pa_tr_gdt
30
31 /* Disable paging to drop us out of lo
32 movl %cr0, %eax
33 andl $~X86_CR0_PG, %eax
34 movl %eax, %cr0
35 ljmpl $__KERNEL32_CS, $pa_machine_re
36
37 SYM_INNER_LABEL(machine_real_restart_paging_of
38 xorl %eax, %eax
39 xorl %edx, %edx
40 movl $MSR_EFER, %ecx
41 wrmsr
42
43 movl %edi, %eax
44
45 #endif /* CONFIG_X86_64 */
46
47 /* Set up the IDT for real mode. */
48 lidtl pa_machine_real_restart_idt
49
50 /*
51 * Set up a GDT from which we can load
52 * mode. The GDT is not used in real
53 * prepare the descriptors.
54 */
55 lgdtl pa_machine_real_restart_gdt
56
57 /*
58 * Load the data segment registers wit
59 */
60 movl $16, %ecx
61 movl %ecx, %ds
62 movl %ecx, %es
63 movl %ecx, %fs
64 movl %ecx, %gs
65 movl %ecx, %ss
66 ljmpw $8, $1f
67 SYM_CODE_END(machine_real_restart_asm)
68
69 /*
70 * This is 16-bit protected mode code to disab
71 * switch to real mode and jump to the BIOS re
72 *
73 * The instruction that switches to real mode
74 * followed immediately by a far jump instruct
75 * valid value for real mode, and flushes the
76 * running instructions that have already been
77 * mode.
78 *
79 * Clears all the flags except ET, especially
80 * (protected-mode enable) and TS (task switch
81 * save). Flushes the TLB after paging has be
82 * NW, to disable the cache on a 486, and inva
83 * is more like the state of a 486 after reset
84 * something else should be done for other chi
85 *
86 * More could be done here to set up the regis
87 * occurred; hopefully real BIOSs don't assume
88 * actual BIOS entry point, anyway (that is at
89 *
90 * Most of this work is probably excessive, bu
91 */
92 .text
93 .code16
94
95 .balign 16
96 machine_real_restart_asm16:
97 1:
98 xorl %ecx, %ecx
99 movl %cr0, %edx
100 andl $0x00000011, %edx
101 orl $0x60000000, %edx
102 movl %edx, %cr0
103 movl %ecx, %cr3
104 movl %cr0, %edx
105 testl $0x60000000, %edx /* If
106 jz 2f
107 wbinvd
108 2:
109 andb $0x10, %dl
110 movl %edx, %cr0
111 LJMPW_RM(3f)
112 3:
113 andw %ax, %ax
114 jz bios
115
116 apm:
117 movw $0x1000, %ax
118 movw %ax, %ss
119 movw $0xf000, %sp
120 movw $0x5307, %ax
121 movw $0x0001, %bx
122 movw $0x0003, %cx
123 int $0x15
124 /* This should never return... */
125
126 bios:
127 ljmpw $0xf000, $0xfff0
128
129 .section ".rodata", "a"
130
131 .balign 16
132 SYM_DATA_START(machine_real_restart_idt)
133 .word 0xffff /* Length - re
134 .long 0 /* Base - real
135 SYM_DATA_END(machine_real_restart_idt)
136
137 .balign 16
138 SYM_DATA_START(machine_real_restart_gdt)
139 /* Self-pointer */
140 .word 0xffff /* Length - re
141 .long pa_machine_real_restart_gdt
142 .word 0
143
144 /*
145 * 16-bit code segment pointing to rea
146 * Selector value 8
147 */
148 .word 0xffff /* Limit */
149 .long 0x9b000000 + pa_real_mode_base
150 .word 0
151
152 /*
153 * 16-bit data segment with the select
154 * base value 0x100; since this is con
155 * semantics we don't have to reload t
156 */
157 .quad GDT_ENTRY(DESC_DATA16, 0x100,
158 SYM_DATA_END(machine_real_restart_gdt)
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