xref: /openbmc/linux/arch/x86/boot/pm.c (revision 97873a3d)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /* -*- linux-c -*- ------------------------------------------------------- *
3  *
4  *   Copyright (C) 1991, 1992 Linus Torvalds
5  *   Copyright 2007 rPath, Inc. - All Rights Reserved
6  *
7  * ----------------------------------------------------------------------- */
8 
9 /*
10  * Prepare the machine for transition to protected mode.
11  */
12 
13 #include "boot.h"
14 #include <asm/segment.h>
15 
16 /*
17  * Invoke the realmode switch hook if present; otherwise
18  * disable all interrupts.
19  */
realmode_switch_hook(void)20 static void realmode_switch_hook(void)
21 {
22 	if (boot_params.hdr.realmode_swtch) {
23 		asm volatile("lcallw *%0"
24 			     : : "m" (boot_params.hdr.realmode_swtch)
25 			     : "eax", "ebx", "ecx", "edx");
26 	} else {
27 		asm volatile("cli");
28 		outb(0x80, 0x70); /* Disable NMI */
29 		io_delay();
30 	}
31 }
32 
33 /*
34  * Disable all interrupts at the legacy PIC.
35  */
mask_all_interrupts(void)36 static void mask_all_interrupts(void)
37 {
38 	outb(0xff, 0xa1);	/* Mask all interrupts on the secondary PIC */
39 	io_delay();
40 	outb(0xfb, 0x21);	/* Mask all but cascade on the primary PIC */
41 	io_delay();
42 }
43 
44 /*
45  * Reset IGNNE# if asserted in the FPU.
46  */
reset_coprocessor(void)47 static void reset_coprocessor(void)
48 {
49 	outb(0, 0xf0);
50 	io_delay();
51 	outb(0, 0xf1);
52 	io_delay();
53 }
54 
55 /*
56  * Set up the GDT
57  */
58 
59 struct gdt_ptr {
60 	u16 len;
61 	u32 ptr;
62 } __attribute__((packed));
63 
setup_gdt(void)64 static void setup_gdt(void)
65 {
66 	/* There are machines which are known to not boot with the GDT
67 	   being 8-byte unaligned.  Intel recommends 16 byte alignment. */
68 	static const u64 boot_gdt[] __attribute__((aligned(16))) = {
69 		/* CS: code, read/execute, 4 GB, base 0 */
70 		[GDT_ENTRY_BOOT_CS] = GDT_ENTRY(0xc09b, 0, 0xfffff),
71 		/* DS: data, read/write, 4 GB, base 0 */
72 		[GDT_ENTRY_BOOT_DS] = GDT_ENTRY(0xc093, 0, 0xfffff),
73 		/* TSS: 32-bit tss, 104 bytes, base 4096 */
74 		/* We only have a TSS here to keep Intel VT happy;
75 		   we don't actually use it for anything. */
76 		[GDT_ENTRY_BOOT_TSS] = GDT_ENTRY(0x0089, 4096, 103),
77 	};
78 	/* Xen HVM incorrectly stores a pointer to the gdt_ptr, instead
79 	   of the gdt_ptr contents.  Thus, make it static so it will
80 	   stay in memory, at least long enough that we switch to the
81 	   proper kernel GDT. */
82 	static struct gdt_ptr gdt;
83 
84 	gdt.len = sizeof(boot_gdt)-1;
85 	gdt.ptr = (u32)&boot_gdt + (ds() << 4);
86 
87 	asm volatile("lgdtl %0" : : "m" (gdt));
88 }
89 
90 /*
91  * Set up the IDT
92  */
setup_idt(void)93 static void setup_idt(void)
94 {
95 	static const struct gdt_ptr null_idt = {0, 0};
96 	asm volatile("lidtl %0" : : "m" (null_idt));
97 }
98 
99 /*
100  * Actual invocation sequence
101  */
go_to_protected_mode(void)102 void go_to_protected_mode(void)
103 {
104 	/* Hook before leaving real mode, also disables interrupts */
105 	realmode_switch_hook();
106 
107 	/* Enable the A20 gate */
108 	if (enable_a20()) {
109 		puts("A20 gate not responding, unable to boot...\n");
110 		die();
111 	}
112 
113 	/* Reset coprocessor (IGNNE#) */
114 	reset_coprocessor();
115 
116 	/* Mask all interrupts in the PIC */
117 	mask_all_interrupts();
118 
119 	/* Actual transition to protected mode... */
120 	setup_idt();
121 	setup_gdt();
122 	protected_mode_jump(boot_params.hdr.code32_start,
123 			    (u32)&boot_params + (ds() << 4));
124 }
125