2 * U-Boot - x86 Startup Code
4 * (C) Copyright 2008-2011
5 * Graeme Russ, <graeme.russ@gmail.com>
8 * Daniel Engström, Omicron Ceti AB, <daniel@omicron.se>
10 * SPDX-License-Identifier: GPL-2.0+
14 #include <asm/global_data.h>
16 #include <asm/processor.h>
17 #include <asm/processor-flags.h>
18 #include <generated/generic-asm-offsets.h>
19 #include <generated/asm-offsets.h>
22 * Define this to boot U-Boot from a 32-bit program which sets the GDT
23 * differently. This can be used to boot directly from any stage of coreboot,
24 * for example, bypassing the normal payload-loading feature.
25 * This is only useful for development.
27 #undef LOAD_FROM_32_BIT
32 .type _start, @function
36 * This is the fail-safe 32-bit bootstrap entry point.
38 * This code is used when booting from another boot loader like
39 * coreboot or EFI. So we repeat some of the same init found in
45 /* Turn off cache (this might require a 486-class CPU) */
47 orl $(X86_CR0_NW | X86_CR0_CD), %eax
51 /* Tell 32-bit code it is being entered from an in-RAM copy */
52 movl $GD_FLG_WARM_BOOT, %ebx
55 * Zero the BIST (Built-In Self Test) value since we don't have it.
56 * It must be 0 or the previous loader would have reported an error.
62 /* Add a way for tools to discover the _start entry point */
67 * This is the 32-bit cold-reset entry point, coming from start16.
68 * Set %ebx to GD_FLG_COLD_BOOT to indicate this.
70 movl $GD_FLG_COLD_BOOT, %ebx
76 /* Save table pointer */
79 #ifdef LOAD_FROM_32_BIT
83 /* Load the segement registers to match the GDT loaded in start16.S */
84 movl $(X86_GDT_ENTRY_32BIT_DS * X86_GDT_ENTRY_SIZE), %eax
91 /* Clear the interrupt vectors */
95 * Critical early platform init - generally not used, we prefer init
96 * to happen later when we have a console, in case something goes
100 .globl early_board_init_ret
101 early_board_init_ret:
102 post_code(POST_START)
104 /* Initialise Cache-As-RAM */
108 #ifndef CONFIG_HAVE_FSP
110 * We now have CONFIG_SYS_CAR_SIZE bytes of Cache-As-RAM (or SRAM,
111 * or fully initialised SDRAM - we really don't care which)
112 * starting at CONFIG_SYS_CAR_ADDR to be used as a temporary stack
113 * and early malloc() area. The MRC requires some space at the top.
115 * Stack grows down from top of CAR. We have:
117 * top-> CONFIG_SYS_CAR_ADDR + CONFIG_SYS_CAR_SIZE
119 * global_data with x86 global descriptor table
122 * bottom-> CONFIG_SYS_CAR_ADDR
124 movl $(CONFIG_SYS_CAR_ADDR + CONFIG_SYS_CAR_SIZE - 4), %esp
125 #ifdef CONFIG_DCACHE_RAM_MRC_VAR_SIZE
126 subl $CONFIG_DCACHE_RAM_MRC_VAR_SIZE, %esp
130 * U-Boot enters here twice. For the first time it comes from
131 * car_init_done() with esp points to a temporary stack and esi
132 * set to zero. For the second time it comes from fsp_init_done()
133 * with esi holding the HOB list address returned by the FSP.
136 /* Set up global data */
138 call board_init_f_alloc_reserve
140 call board_init_f_init_reserve
142 #ifdef CONFIG_DEBUG_UART
146 /* Get address of global_data */
148 #ifdef CONFIG_HAVE_FSP
149 /* Store the HOB list if we have one */
152 movl %esi, GD_HOB_LIST(%edx)
155 * After fsp_init() returns, the stack has already been switched to a
156 * place within system memory as defined by CONFIG_FSP_TEMP_RAM_ADDR.
157 * Enlarge the size of malloc() pool before relocation since we have
158 * plenty of memory now.
160 subl $CONFIG_FSP_SYS_MALLOC_F_LEN, %esp
161 movl %esp, GD_MALLOC_BASE(%edx)
164 /* Store table pointer */
165 movl %esi, GD_TABLE(%edx)
168 movl %ebp, GD_BIST(%edx)
170 /* Set parameter to board_init_f() to boot flags */
171 post_code(POST_START_DONE)
177 /* indicate (lack of) progress */
181 .globl board_init_f_r_trampoline
182 .type board_init_f_r_trampoline, @function
183 board_init_f_r_trampoline:
185 * SDRAM has been initialised, U-Boot code has been copied into
186 * RAM, BSS has been cleared and relocation adjustments have been
187 * made. It is now time to jump into the in-RAM copy of U-Boot
189 * %eax = Address of top of new stack
192 /* Stack grows down from top of SDRAM */
195 /* See if we need to disable CAR */
197 movl $car_uninit, %eax
203 /* Re-enter U-Boot by calling board_init_f_r() */
215 .p2align 2 /* force 4-byte alignment */
217 /* Add a multiboot header so U-Boot can be loaded by GRUB2 */
224 .long -0x1BADB002 - (1 << 16)
226 .long multiboot_header - _x86boot_start + CONFIG_SYS_TEXT_BASE
228 .long CONFIG_SYS_TEXT_BASE
234 .long CONFIG_SYS_TEXT_BASE
236 #ifdef LOAD_FROM_32_BIT
238 * The following Global Descriptor Table is just enough to get us into
239 * 'Flat Protected Mode' - It will be discarded as soon as the final
240 * GDT is setup in a safe location in RAM
243 .word 0x1f /* limit (31 bytes = 4 GDT entries - 1) */
244 .long gdt_rom2 /* base */
246 /* Some CPUs are picky about GDT alignment... */
257 * 0x18 32bit data/stack
259 /* The NULL Desciptor - Mandatory */
260 .word 0x0000 /* limit_low */
261 .word 0x0000 /* base_low */
262 .byte 0x00 /* base_middle */
263 .byte 0x00 /* access */
264 .byte 0x00 /* flags + limit_high */
265 .byte 0x00 /* base_high */
267 /* Unused Desciptor - (matches Linux) */
268 .word 0x0000 /* limit_low */
269 .word 0x0000 /* base_low */
270 .byte 0x00 /* base_middle */
271 .byte 0x00 /* access */
272 .byte 0x00 /* flags + limit_high */
273 .byte 0x00 /* base_high */
276 * The Code Segment Descriptor:
277 * - Base = 0x00000000
279 * - Access = Present, Ring 0, Exec (Code), Readable
280 * - Flags = 4kB Granularity, 32-bit
282 .word 0xffff /* limit_low */
283 .word 0x0000 /* base_low */
284 .byte 0x00 /* base_middle */
285 .byte 0x9b /* access */
286 .byte 0xcf /* flags + limit_high */
287 .byte 0x00 /* base_high */
290 * The Data Segment Descriptor:
291 * - Base = 0x00000000
293 * - Access = Present, Ring 0, Non-Exec (Data), Writable
294 * - Flags = 4kB Granularity, 32-bit
296 .word 0xffff /* limit_low */
297 .word 0x0000 /* base_low */
298 .byte 0x00 /* base_middle */
299 .byte 0x93 /* access */
300 .byte 0xcf /* flags + limit_high */
301 .byte 0x00 /* base_high */