1/* -*- linux-c -*- ------------------------------------------------------- *
2 *
3 *   Copyright (C) 1991, 1992 Linus Torvalds
4 *   Copyright 2007 rPath, Inc. - All Rights Reserved
5 *
6 *   This file is part of the Linux kernel, and is made available under
7 *   the terms of the GNU General Public License version 2.
8 *
9 * ----------------------------------------------------------------------- */
10
11/*
12 * Prepare the machine for transition to protected mode.
13 */
14
15#include "boot.h"
16#include <asm/segment.h>
17
18/*
19 * Invoke the realmode switch hook if present; otherwise
20 * disable all interrupts.
21 */
22static void realmode_switch_hook(void)
23{
24	if (boot_params.hdr.realmode_swtch) {
25		asm volatile("lcallw *%0"
26			     : : "m" (boot_params.hdr.realmode_swtch)
27			     : "eax", "ebx", "ecx", "edx");
28	} else {
29		asm volatile("cli");
30		outb(0x80, 0x70); /* Disable NMI */
31		io_delay();
32	}
33}
34
35/*
36 * Disable all interrupts at the legacy PIC.
37 */
38static void mask_all_interrupts(void)
39{
40	outb(0xff, 0xa1);	/* Mask all interrupts on the secondary PIC */
41	io_delay();
42	outb(0xfb, 0x21);	/* Mask all but cascade on the primary PIC */
43	io_delay();
44}
45
46/*
47 * Reset IGNNE# if asserted in the FPU.
48 */
49static void reset_coprocessor(void)
50{
51	outb(0, 0xf0);
52	io_delay();
53	outb(0, 0xf1);
54	io_delay();
55}
56
57/*
58 * Set up the GDT
59 */
60
61struct gdt_ptr {
62	u16 len;
63	u32 ptr;
64} __attribute__((packed));
65
66static void setup_gdt(void)
67{
68	/* There are machines which are known to not boot with the GDT
69	   being 8-byte unaligned.  Intel recommends 16 byte alignment. */
70	static const u64 boot_gdt[] __attribute__((aligned(16))) = {
71		/* CS: code, read/execute, 4 GB, base 0 */
72		[GDT_ENTRY_BOOT_CS] = GDT_ENTRY(0xc09b, 0, 0xfffff),
73		/* DS: data, read/write, 4 GB, base 0 */
74		[GDT_ENTRY_BOOT_DS] = GDT_ENTRY(0xc093, 0, 0xfffff),
75		/* TSS: 32-bit tss, 104 bytes, base 4096 */
76		/* We only have a TSS here to keep Intel VT happy;
77		   we don't actually use it for anything. */
78		[GDT_ENTRY_BOOT_TSS] = GDT_ENTRY(0x0089, 4096, 103),
79	};
80	/* Xen HVM incorrectly stores a pointer to the gdt_ptr, instead
81	   of the gdt_ptr contents.  Thus, make it static so it will
82	   stay in memory, at least long enough that we switch to the
83	   proper kernel GDT. */
84	static struct gdt_ptr gdt;
85
86	gdt.len = sizeof(boot_gdt)-1;
87	gdt.ptr = (u32)&boot_gdt + (ds() << 4);
88
89	asm volatile("lgdtl %0" : : "m" (gdt));
90}
91
92/*
93 * Set up the IDT
94 */
95static void setup_idt(void)
96{
97	static const struct gdt_ptr null_idt = {0, 0};
98	asm volatile("lidtl %0" : : "m" (null_idt));
99}
100
101/*
102 * Actual invocation sequence
103 */
104void go_to_protected_mode(void)
105{
106	/* Hook before leaving real mode, also disables interrupts */
107	realmode_switch_hook();
108
109	/* Enable the A20 gate */
110	if (enable_a20()) {
111		puts("A20 gate not responding, unable to boot...\n");
112		die();
113	}
114
115	/* Reset coprocessor (IGNNE#) */
116	reset_coprocessor();
117
118	/* Mask all interrupts in the PIC */
119	mask_all_interrupts();
120
121	/* Actual transition to protected mode... */
122	setup_idt();
123	setup_gdt();
124	protected_mode_jump(boot_params.hdr.code32_start,
125			    (u32)&boot_params + (ds() << 4));
126}
127