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/global_data.h> 13#include <asm/processor-flags.h> 14 15#define BOOT_SEG 0xffff0000 /* linear segment of boot code */ 16#define a32 .byte 0x67; 17#define o32 .byte 0x66; 18 19.section .start16, "ax" 20.code16 21.globl start16 22start16: 23 /* Save BIST */ 24 movl %eax, %ecx 25 26 /* Set the Cold Boot / Hard Reset flag */ 27 movl $GD_FLG_COLD_BOOT, %ebx 28 29 xorl %eax, %eax 30 movl %eax, %cr3 /* Invalidate TLB */ 31 32 /* Turn off cache (this might require a 486-class CPU) */ 33 movl %cr0, %eax 34 orl $(X86_CR0_NW | X86_CR0_CD), %eax 35 movl %eax, %cr0 36 wbinvd 37 38 /* load the temporary Global Descriptor Table */ 39o32 cs lidt idt_ptr 40o32 cs lgdt gdt_ptr 41 42 /* Now, we enter protected mode */ 43 movl %cr0, %eax 44 orl $X86_CR0_PE, %eax 45 movl %eax, %cr0 46 47 /* Flush the prefetch queue */ 48 jmp ff 49ff: 50 51 /* Finally restore BIST and jump to the 32-bit initialization code */ 52 movw $code32start, %ax 53 movw %ax, %bp 54 movl %ecx, %eax 55o32 cs ljmp *(%bp) 56 57 /* 48-bit far pointer */ 58code32start: 59 .long _start /* offset */ 60 .word 0x10 /* segment */ 61 62idt_ptr: 63 .word 0 /* limit */ 64 .long 0 /* base */ 65 66 /* 67 * The following Global Descriptor Table is just enough to get us into 68 * 'Flat Protected Mode' - It will be discarded as soon as the final 69 * GDT is setup in a safe location in RAM 70 */ 71gdt_ptr: 72 .word 0x1f /* limit (31 bytes = 4 GDT entries - 1) */ 73 .long BOOT_SEG + gdt_rom /* base */ 74 75 /* Some CPUs are picky about GDT alignment... */ 76 .align 16 77.globl gdt_rom 78gdt_rom: 79 /* 80 * The GDT table ... 81 * 82 * Selector Type 83 * 0x00 NULL 84 * 0x08 Unused 85 * 0x10 32bit code 86 * 0x18 32bit data/stack 87 */ 88 /* The NULL Desciptor - Mandatory */ 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 /* Unused Desciptor - (matches Linux) */ 97 .word 0x0000 /* limit_low */ 98 .word 0x0000 /* base_low */ 99 .byte 0x00 /* base_middle */ 100 .byte 0x00 /* access */ 101 .byte 0x00 /* flags + limit_high */ 102 .byte 0x00 /* base_high */ 103 104 /* 105 * The Code Segment Descriptor: 106 * - Base = 0x00000000 107 * - Size = 4GB 108 * - Access = Present, Ring 0, Exec (Code), Readable 109 * - Flags = 4kB Granularity, 32-bit 110 */ 111 .word 0xffff /* limit_low */ 112 .word 0x0000 /* base_low */ 113 .byte 0x00 /* base_middle */ 114 .byte 0x9b /* access */ 115 .byte 0xcf /* flags + limit_high */ 116 .byte 0x00 /* base_high */ 117 118 /* 119 * The Data Segment Descriptor: 120 * - Base = 0x00000000 121 * - Size = 4GB 122 * - Access = Present, Ring 0, Non-Exec (Data), Writable 123 * - Flags = 4kB Granularity, 32-bit 124 */ 125 .word 0xffff /* limit_low */ 126 .word 0x0000 /* base_low */ 127 .byte 0x00 /* base_middle */ 128 .byte 0x93 /* access */ 129 .byte 0xcf /* flags + limit_high */ 130 .byte 0x00 /* base_high */ 131