xref: /openbmc/linux/arch/arm/boot/bootp/init.S (revision 790756c7)
1/* SPDX-License-Identifier: GPL-2.0-only */
2/*
3 *  linux/arch/arm/boot/bootp/init.S
4 *
5 *  Copyright (C) 2000-2003 Russell King.
6 *
7 *  "Header" file for splitting kernel + initrd.  Note that we pass
8 *  r0 through to r3 straight through.
9 *
10 *  This demonstrates how to append code to the start of the kernel
11 *  zImage, and boot the kernel without copying it around.  This
12 *  example would be simpler; if we didn't have an object of unknown
13 *  size immediately following the kernel, we could build this into
14 *  a binary blob, and concatenate the zImage using the cat command.
15 */
16		.section .start, "ax"
17		.type	_start, #function
18		.globl	_start
19
20_start:		add	lr, pc, #-0x8		@ lr = current load addr
21		adr	r13, data
22		ldmia	r13!, {r4-r6}		@ r5 = dest, r6 = length
23		add	r4, r4, lr		@ r4 = initrd_start + load addr
24		bl	move			@ move the initrd
25
26/*
27 * Setup the initrd parameters to pass to the kernel.  This can only be
28 * passed in via the tagged list.
29 */
30		ldmia	r13, {r5-r9}		@ get size and addr of initrd
31						@ r5 = ATAG_CORE
32						@ r6 = ATAG_INITRD2
33						@ r7 = initrd start
34						@ r8 = initrd end
35						@ r9 = param_struct address
36
37		ldr	r10, [r9, #4]		@ get first tag
38		teq	r10, r5			@ is it ATAG_CORE?
39/*
40 * If we didn't find a valid tag list, create a dummy ATAG_CORE entry.
41 */
42		movne	r10, #0			@ terminator
43		movne	r4, #2			@ Size of this entry (2 words)
44		stmiane	r9, {r4, r5, r10}	@ Size, ATAG_CORE, terminator
45
46/*
47 * find the end of the tag list, and then add an INITRD tag on the end.
48 * If there is already an INITRD tag, then we ignore it; the last INITRD
49 * tag takes precedence.
50 */
51taglist:	ldr	r10, [r9, #0]		@ tag length
52		teq	r10, #0			@ last tag (zero length)?
53		addne	r9, r9, r10, lsl #2
54		bne	taglist
55
56		mov	r5, #4			@ Size of initrd tag (4 words)
57		stmia	r9, {r5, r6, r7, r8, r10}
58		b	kernel_start		@ call kernel
59
60/*
61 * Move the block of memory length r6 from address r4 to address r5
62 */
63move:		ldmia	r4!, {r7 - r10}		@ move 32-bytes at a time
64		stmia	r5!, {r7 - r10}
65		ldmia	r4!, {r7 - r10}
66		stmia	r5!, {r7 - r10}
67		subs	r6, r6, #8 * 4
68		bcs	move
69		mov	pc, lr
70
71		.size	_start, . - _start
72
73		.align
74
75		.type	data,#object
76data:		.word	initrd_start		@ source initrd address
77		.word	initrd_phys		@ destination initrd address
78		.word	initrd_size		@ initrd size
79
80		.word	0x54410001		@ r5 = ATAG_CORE
81		.word	0x54420005		@ r6 = ATAG_INITRD2
82		.word	initrd_phys		@ r7
83		.word	initrd_size		@ r8
84		.word	params_phys		@ r9
85		.size	data, . - data
86