xref: /openbmc/u-boot/arch/arm/lib/crt0.S (revision 35f9d9bd)
1/* SPDX-License-Identifier: GPL-2.0+ */
2/*
3 *  crt0 - C-runtime startup Code for ARM U-Boot
4 *
5 *  Copyright (c) 2012  Albert ARIBAUD <albert.u.boot@aribaud.net>
6 */
7
8#include <config.h>
9#include <asm-offsets.h>
10#include <linux/linkage.h>
11#include <asm/assembler.h>
12
13/*
14 * This file handles the target-independent stages of the U-Boot
15 * start-up where a C runtime environment is needed. Its entry point
16 * is _main and is branched into from the target's start.S file.
17 *
18 * _main execution sequence is:
19 *
20 * 1. Set up initial environment for calling board_init_f().
21 *    This environment only provides a stack and a place to store
22 *    the GD ('global data') structure, both located in some readily
23 *    available RAM (SRAM, locked cache...). In this context, VARIABLE
24 *    global data, initialized or not (BSS), are UNAVAILABLE; only
25 *    CONSTANT initialized data are available. GD should be zeroed
26 *    before board_init_f() is called.
27 *
28 * 2. Call board_init_f(). This function prepares the hardware for
29 *    execution from system RAM (DRAM, DDR...) As system RAM may not
30 *    be available yet, , board_init_f() must use the current GD to
31 *    store any data which must be passed on to later stages. These
32 *    data include the relocation destination, the future stack, and
33 *    the future GD location.
34 *
35 * 3. Set up intermediate environment where the stack and GD are the
36 *    ones allocated by board_init_f() in system RAM, but BSS and
37 *    initialized non-const data are still not available.
38 *
39 * 4a.For U-Boot proper (not SPL), call relocate_code(). This function
40 *    relocates U-Boot from its current location into the relocation
41 *    destination computed by board_init_f().
42 *
43 * 4b.For SPL, board_init_f() just returns (to crt0). There is no
44 *    code relocation in SPL.
45 *
46 * 5. Set up final environment for calling board_init_r(). This
47 *    environment has BSS (initialized to 0), initialized non-const
48 *    data (initialized to their intended value), and stack in system
49 *    RAM (for SPL moving the stack and GD into RAM is optional - see
50 *    CONFIG_SPL_STACK_R). GD has retained values set by board_init_f().
51 *
52 * 6. For U-Boot proper (not SPL), some CPUs have some work left to do
53 *    at this point regarding memory, so call c_runtime_cpu_setup.
54 *
55 * 7. Branch to board_init_r().
56 *
57 * For more information see 'Board Initialisation Flow in README.
58 */
59
60/*
61 * entry point of crt0 sequence
62 */
63
64ENTRY(_main)
65
66/*
67 * Set up initial C runtime environment and call board_init_f(0).
68 */
69
70#if defined(CONFIG_SPL_BUILD) && defined(CONFIG_SPL_STACK)
71	ldr	r0, =(CONFIG_SPL_STACK)
72#else
73	ldr	r0, =(CONFIG_SYS_INIT_SP_ADDR)
74#endif
75	bic	r0, r0, #7	/* 8-byte alignment for ABI compliance */
76	mov	sp, r0
77	bl	board_init_f_alloc_reserve
78	mov	sp, r0
79	/* set up gd here, outside any C code */
80	mov	r9, r0
81	bl	board_init_f_init_reserve
82
83	mov	r0, #0
84	bl	board_init_f
85
86#if ! defined(CONFIG_SPL_BUILD)
87
88/*
89 * Set up intermediate environment (new sp and gd) and call
90 * relocate_code(addr_moni). Trick here is that we'll return
91 * 'here' but relocated.
92 */
93
94	ldr	r0, [r9, #GD_START_ADDR_SP]	/* sp = gd->start_addr_sp */
95	bic	r0, r0, #7	/* 8-byte alignment for ABI compliance */
96	mov	sp, r0
97	ldr	r9, [r9, #GD_BD]		/* r9 = gd->bd */
98	sub	r9, r9, #GD_SIZE		/* new GD is below bd */
99
100	adr	lr, here
101	ldr	r0, [r9, #GD_RELOC_OFF]		/* r0 = gd->reloc_off */
102	add	lr, lr, r0
103#if defined(CONFIG_CPU_V7M)
104	orr	lr, #1				/* As required by Thumb-only */
105#endif
106	ldr	r0, [r9, #GD_RELOCADDR]		/* r0 = gd->relocaddr */
107	b	relocate_code
108here:
109/*
110 * now relocate vectors
111 */
112
113	bl	relocate_vectors
114
115/* Set up final (full) environment */
116
117	bl	c_runtime_cpu_setup	/* we still call old routine here */
118#endif
119#if !defined(CONFIG_SPL_BUILD) || defined(CONFIG_SPL_FRAMEWORK)
120# ifdef CONFIG_SPL_BUILD
121	/* Use a DRAM stack for the rest of SPL, if requested */
122	bl	spl_relocate_stack_gd
123	cmp	r0, #0
124	movne	sp, r0
125	movne	r9, r0
126# endif
127	ldr	r0, =__bss_start	/* this is auto-relocated! */
128
129#ifdef CONFIG_USE_ARCH_MEMSET
130	ldr	r3, =__bss_end		/* this is auto-relocated! */
131	mov	r1, #0x00000000		/* prepare zero to clear BSS */
132
133	subs	r2, r3, r0		/* r2 = memset len */
134	bl	memset
135#else
136	ldr	r1, =__bss_end		/* this is auto-relocated! */
137	mov	r2, #0x00000000		/* prepare zero to clear BSS */
138
139clbss_l:cmp	r0, r1			/* while not at end of BSS */
140	strlo	r2, [r0]		/* clear 32-bit BSS word */
141	addlo	r0, r0, #4		/* move to next */
142	blo	clbss_l
143#endif
144
145#if ! defined(CONFIG_SPL_BUILD)
146	bl coloured_LED_init
147	bl red_led_on
148#endif
149	/* call board_init_r(gd_t *id, ulong dest_addr) */
150	mov     r0, r9                  /* gd_t */
151	ldr	r1, [r9, #GD_RELOCADDR]	/* dest_addr */
152	/* call board_init_r */
153#if CONFIG_IS_ENABLED(SYS_THUMB_BUILD)
154	ldr	lr, =board_init_r	/* this is auto-relocated! */
155	bx	lr
156#else
157	ldr	pc, =board_init_r	/* this is auto-relocated! */
158#endif
159	/* we should not return here. */
160#endif
161
162ENDPROC(_main)
163