1/* SPDX-License-Identifier: GPL-2.0+ */
2/*
3 *  U-Boot - x86 Startup Code
4 *
5 * (C) Copyright 2008-2011
6 * Graeme Russ, <graeme.russ@gmail.com>
7 *
8 * (C) Copyright 2002,2003
9 * Daniel Engström, Omicron Ceti AB, <daniel@omicron.se>
10 */
11
12#include <asm/processor-flags.h>
13
14#define BOOT_SEG	0xffff0000	/* linear segment of boot code */
15
16.section .start16, "ax"
17.code16
18.globl start16
19start16:
20	/* Save BIST */
21	movl	%eax, %ecx
22
23	xorl	%eax, %eax
24	movl	%eax, %cr3	/* Invalidate TLB */
25
26	/* Turn off cache (this might require a 486-class CPU) */
27	movl	%cr0, %eax
28	orl	$(X86_CR0_NW | X86_CR0_CD), %eax
29	movl	%eax, %cr0
30	wbinvd
31
32	/* load the temporary Global Descriptor Table */
33data32 cs	lidt	idt_ptr
34data32 cs	lgdt	gdt_ptr
35
36	/* Now, we enter protected mode */
37	movl	%cr0, %eax
38	orl	$X86_CR0_PE, %eax
39	movl	%eax, %cr0
40
41	/* Flush the prefetch queue */
42	jmp	ff
43ff:
44
45	/* Finally restore BIST and jump to the 32-bit initialization code */
46	movl	%ecx, %eax
47data32 cs	ljmp	*code32start
48
49	/* 48-bit far pointer */
50code32start:
51	.long	_start		/* offset */
52	.word	0x10		/* segment */
53
54idt_ptr:
55	.word	0		/* limit */
56	.long	0		/* base */
57
58	/*
59	 * The following Global Descriptor Table is just enough to get us into
60	 * 'Flat Protected Mode' - It will be discarded as soon as the final
61	 * GDT is setup in a safe location in RAM
62	 */
63gdt_ptr:
64	.word	0x1f		/* limit (31 bytes = 4 GDT entries - 1) */
65	.long	BOOT_SEG + gdt_rom	/* base */
66
67	/* Some CPUs are picky about GDT alignment... */
68	.align	16
69.globl gdt_rom
70gdt_rom:
71	/*
72	 * The GDT table ...
73	 *
74	 *	 Selector	Type
75	 *	 0x00		NULL
76	 *	 0x08		Unused
77	 *	 0x10		32bit code
78	 *	 0x18		32bit data/stack
79	 */
80	/* The NULL Desciptor - Mandatory */
81	.word	0x0000		/* limit_low */
82	.word	0x0000		/* base_low */
83	.byte	0x00		/* base_middle */
84	.byte	0x00		/* access */
85	.byte	0x00		/* flags + limit_high */
86	.byte	0x00		/* base_high */
87
88	/* Unused Desciptor - (matches Linux) */
89	.word	0x0000		/* limit_low */
90	.word	0x0000		/* base_low */
91	.byte	0x00		/* base_middle */
92	.byte	0x00		/* access */
93	.byte	0x00		/* flags + limit_high */
94	.byte	0x00		/* base_high */
95
96	/*
97	 * The Code Segment Descriptor:
98	 * - Base   = 0x00000000
99	 * - Size   = 4GB
100	 * - Access = Present, Ring 0, Exec (Code), Readable
101	 * - Flags  = 4kB Granularity, 32-bit
102	 */
103	.word	0xffff		/* limit_low */
104	.word	0x0000		/* base_low */
105	.byte	0x00		/* base_middle */
106	.byte	0x9b		/* access */
107	.byte	0xcf		/* flags + limit_high */
108	.byte	0x00		/* base_high */
109
110	/*
111	 * The Data Segment Descriptor:
112	 * - Base   = 0x00000000
113	 * - Size   = 4GB
114	 * - Access = Present, Ring 0, Non-Exec (Data), Writable
115	 * - Flags  = 4kB Granularity, 32-bit
116	 */
117	.word	0xffff		/* limit_low */
118	.word	0x0000		/* base_low */
119	.byte	0x00		/* base_middle */
120	.byte	0x93		/* access */
121	.byte	0xcf		/* flags + limit_high */
122	.byte	0x00		/* base_high */
123