xref: /openbmc/u-boot/arch/x86/cpu/start.S (revision 20c700f8)
1/*
2 *  U-Boot - x86 Startup Code
3 *
4 * (C) Copyright 2008-2011
5 * Graeme Russ, <graeme.russ@gmail.com>
6 *
7 * (C) Copyright 2002
8 * Daniel Engström, Omicron Ceti AB, <daniel@omicron.se>
9 *
10 * SPDX-License-Identifier:	GPL-2.0+
11 */
12
13#include <config.h>
14#include <asm/global_data.h>
15#include <asm/post.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>
20
21/*
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.
26 */
27#undef LOAD_FROM_32_BIT
28
29.section .text
30.code32
31.globl _start
32.type _start, @function
33.globl _x86boot_start
34_x86boot_start:
35	/*
36	 * This is the fail-safe 32-bit bootstrap entry point.
37	 *
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
40	 * start16.
41	 */
42	cli
43	cld
44
45	/* Turn off cache (this might require a 486-class CPU) */
46	movl	%cr0, %eax
47	orl	$(X86_CR0_NW | X86_CR0_CD), %eax
48	movl	%eax, %cr0
49	wbinvd
50
51	/* Tell 32-bit code it is being entered from an in-RAM copy */
52	movl	$GD_FLG_WARM_BOOT, %ebx
53
54	/*
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.
57	 */
58	movl	$0, %ebp
59
60	jmp	1f
61
62	/* Add a way for tools to discover the _start entry point */
63	.align	4
64	.long	0x12345678
65_start:
66	/*
67	 * This is the 32-bit cold-reset entry point, coming from start16.
68	 * Set %ebx to GD_FLG_COLD_BOOT to indicate this.
69	 */
70	movl	$GD_FLG_COLD_BOOT, %ebx
71
72	/* Save BIST */
73	movl	%eax, %ebp
741:
75
76	/* Save table pointer */
77	movl	%ecx, %esi
78
79#ifdef LOAD_FROM_32_BIT
80	lgdt	gdt_ptr2
81#endif
82
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
85	movw	%ax, %fs
86	movw	%ax, %ds
87	movw	%ax, %gs
88	movw	%ax, %es
89	movw	%ax, %ss
90
91	/* Clear the interrupt vectors */
92	lidt	blank_idt_ptr
93
94	/*
95	 * Critical early platform init - generally not used, we prefer init
96	 * to happen later when we have a console, in case something goes
97	 * wrong.
98	 */
99	jmp	early_board_init
100.globl early_board_init_ret
101early_board_init_ret:
102	post_code(POST_START)
103
104	/* Initialise Cache-As-RAM */
105	jmp	car_init
106.globl car_init_ret
107car_init_ret:
108#ifndef CONFIG_HAVE_FSP
109	/*
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.
114	 *
115	 * Stack grows down from top of CAR. We have:
116	 *
117	 * top-> CONFIG_SYS_CAR_ADDR + CONFIG_SYS_CAR_SIZE
118	 *	MRC area
119	 *	global_data with x86 global descriptor table
120	 *	early malloc area
121	 *	stack
122	 * bottom-> CONFIG_SYS_CAR_ADDR
123	 */
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
127#endif
128#else
129	/*
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.
134	 */
135#endif
136	/* Set up global data */
137	mov	%esp, %eax
138	call	board_init_f_alloc_reserve
139	mov	%eax, %esp
140	call	board_init_f_init_reserve
141
142#ifdef CONFIG_DEBUG_UART
143	call	debug_uart_init
144#endif
145
146	/* Get address of global_data */
147	mov	%fs:0, %edx
148#ifdef CONFIG_HAVE_FSP
149	/* Store the HOB list if we have one */
150	test	%esi, %esi
151	jz	skip_hob
152	movl	%esi, GD_HOB_LIST(%edx)
153
154	/*
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.
159	 */
160	subl	$CONFIG_FSP_SYS_MALLOC_F_LEN, %esp
161	movl	%esp, GD_MALLOC_BASE(%edx)
162skip_hob:
163#else
164	/* Store table pointer */
165	movl	%esi, GD_TABLE(%edx)
166#endif
167	/* Store BIST */
168	movl	%ebp, GD_BIST(%edx)
169
170	/* Set parameter to board_init_f() to boot flags */
171	post_code(POST_START_DONE)
172	xorl	%eax, %eax
173
174	/* Enter, U-Boot! */
175	call	board_init_f
176
177	/* indicate (lack of) progress */
178	movw	$0x85, %ax
179	jmp	die
180
181.globl board_init_f_r_trampoline
182.type board_init_f_r_trampoline, @function
183board_init_f_r_trampoline:
184	/*
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
188	 *
189	 * %eax = Address of top of new stack
190	 */
191
192	/* Stack grows down from top of SDRAM */
193	movl	%eax, %esp
194
195	/* See if we need to disable CAR */
196.weak	car_uninit
197	movl	$car_uninit, %eax
198	cmpl	$0, %eax
199	jz	1f
200
201	call	car_uninit
2021:
203	/* Re-enter U-Boot by calling board_init_f_r() */
204	call	board_init_f_r
205
206die:
207	hlt
208	jmp	die
209	hlt
210
211blank_idt_ptr:
212	.word	0		/* limit */
213	.long	0		/* base */
214
215	.p2align	2	/* force 4-byte alignment */
216
217	/* Add a multiboot header so U-Boot can be loaded by GRUB2 */
218multiboot_header:
219	/* magic */
220	.long	0x1badb002
221	/* flags */
222	.long	(1 << 16)
223	/* checksum */
224	.long	-0x1BADB002 - (1 << 16)
225	/* header addr */
226	.long	multiboot_header - _x86boot_start + CONFIG_SYS_TEXT_BASE
227	/* load addr */
228	.long	CONFIG_SYS_TEXT_BASE
229	/* load end addr */
230	.long	0
231	/* bss end addr */
232	.long	0
233	/* entry addr */
234	.long	CONFIG_SYS_TEXT_BASE
235
236#ifdef LOAD_FROM_32_BIT
237	/*
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
241	 */
242gdt_ptr2:
243	.word	0x1f		/* limit (31 bytes = 4 GDT entries - 1) */
244	.long	gdt_rom2	/* base */
245
246	/* Some CPUs are picky about GDT alignment... */
247	.align	16
248.globl gdt_rom2
249gdt_rom2:
250	/*
251	 * The GDT table ...
252	 *
253	 *	 Selector	Type
254	 *	 0x00		NULL
255	 *	 0x08		Unused
256	 *	 0x10		32bit code
257	 *	 0x18		32bit data/stack
258	 */
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 */
266
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 */
274
275	/*
276	 * The Code Segment Descriptor:
277	 * - Base   = 0x00000000
278	 * - Size   = 4GB
279	 * - Access = Present, Ring 0, Exec (Code), Readable
280	 * - Flags  = 4kB Granularity, 32-bit
281	 */
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 */
288
289	/*
290	 * The Data Segment Descriptor:
291	 * - Base   = 0x00000000
292	 * - Size   = 4GB
293	 * - Access = Present, Ring 0, Non-Exec (Data), Writable
294	 * - Flags  = 4kB Granularity, 32-bit
295	 */
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 */
302#endif
303