xref: /openbmc/linux/arch/xtensa/kernel/head.S (revision 84953f96) 
1/*
2 * arch/xtensa/kernel/head.S
3 *
4 * Xtensa Processor startup code.
5 *
6 * This file is subject to the terms and conditions of the GNU General Public
7 * License.  See the file "COPYING" in the main directory of this archive
8 * for more details.
9 *
10 * Copyright (C) 2001 - 2008 Tensilica Inc.
11 *
12 * Chris Zankel <chris@zankel.net>
13 * Marc Gauthier <marc@tensilica.com, marc@alumni.uwaterloo.ca>
14 * Joe Taylor <joe@tensilica.com, joetylr@yahoo.com>
15 * Kevin Chea
16 */
17
18#include <asm/processor.h>
19#include <asm/page.h>
20#include <asm/cacheasm.h>
21#include <asm/initialize_mmu.h>
22
23#include <linux/init.h>
24#include <linux/linkage.h>
25
26/*
27 * This module contains the entry code for kernel images. It performs the
28 * minimal setup needed to call the generic C routines.
29 *
30 * Prerequisites:
31 *
32 * - The kernel image has been loaded to the actual address where it was
33 *   compiled to.
34 * - a2 contains either 0 or a pointer to a list of boot parameters.
35 *   (see setup.c for more details)
36 *
37 */
38
39/*
40 *  _start
41 *
42 *  The bootloader passes a pointer to a list of boot parameters in a2.
43 */
44
45	/* The first bytes of the kernel image must be an instruction, so we
46	 * manually allocate and define the literal constant we need for a jx
47	 * instruction.
48	 */
49
50	__HEAD
51	.begin	no-absolute-literals
52
53ENTRY(_start)
54
55	/* Preserve the pointer to the boot parameter list in EXCSAVE_1 */
56	wsr     a2, excsave1
57	_j	_SetupMMU
58
59	.align	4
60	.literal_position
61.Lstartup:
62	.word	_startup
63
64	.align	4
65	.global _SetupMMU
66_SetupMMU:
67	Offset = _SetupMMU - _start
68
69#ifdef CONFIG_INITIALIZE_XTENSA_MMU_INSIDE_VMLINUX
70	initialize_mmu
71#if defined(CONFIG_MMU) && XCHAL_HAVE_PTP_MMU && XCHAL_HAVE_SPANNING_WAY
72	rsr	a2, excsave1
73	movi	a3, 0x08000000
74	bgeu	a2, a3, 1f
75	movi	a3, 0xd0000000
76	add	a2, a2, a3
77	wsr	a2, excsave1
781:
79#endif
80#endif
81	.end	no-absolute-literals
82
83	l32r	a0, .Lstartup
84	jx	a0
85
86ENDPROC(_start)
87
88	__INIT
89	.literal_position
90
91ENTRY(_startup)
92
93	/* Disable interrupts and exceptions. */
94
95	movi	a0, LOCKLEVEL
96	wsr	a0, ps
97
98	/* Start with a fresh windowbase and windowstart.  */
99
100	movi	a1, 1
101	movi	a0, 0
102	wsr	a1, windowstart
103	wsr	a0, windowbase
104	rsync
105
106	/* Set a0 to 0 for the remaining initialization. */
107
108	movi	a0, 0
109
110	/* Clear debugging registers. */
111
112#if XCHAL_HAVE_DEBUG
113#if XCHAL_NUM_IBREAK > 0
114	wsr	a0, ibreakenable
115#endif
116	wsr	a0, icount
117	movi	a1, 15
118	wsr	a0, icountlevel
119
120	.set	_index, 0
121	.rept	XCHAL_NUM_DBREAK - 1
122	wsr	a0, SREG_DBREAKC + _index
123	.set	_index, _index + 1
124	.endr
125#endif
126
127	/* Clear CCOUNT (not really necessary, but nice) */
128
129	wsr	a0, ccount	# not really necessary, but nice
130
131	/* Disable zero-loops. */
132
133#if XCHAL_HAVE_LOOPS
134	wsr	a0, lcount
135#endif
136
137	/* Disable all timers. */
138
139	.set	_index, 0
140	.rept	XCHAL_NUM_TIMERS
141	wsr	a0, SREG_CCOMPARE + _index
142	.set	_index, _index + 1
143	.endr
144
145	/* Interrupt initialization. */
146
147	movi	a2, XCHAL_INTTYPE_MASK_SOFTWARE | XCHAL_INTTYPE_MASK_EXTERN_EDGE
148	wsr	a0, intenable
149	wsr	a2, intclear
150
151	/* Disable coprocessors. */
152
153#if XCHAL_HAVE_CP
154	wsr	a0, cpenable
155#endif
156
157	/* Set PS.INTLEVEL=LOCKLEVEL, PS.WOE=0, kernel stack, PS.EXCM=0
158	 *
159	 * Note: PS.EXCM must be cleared before using any loop
160	 *	 instructions; otherwise, they are silently disabled, and
161	 * 	 at most one iteration of the loop is executed.
162	 */
163
164	movi	a1, LOCKLEVEL
165	wsr	a1, ps
166	rsync
167
168	/*  Initialize the caches.
169	 *  a2, a3 are just working registers (clobbered).
170	 */
171
172#if XCHAL_DCACHE_LINE_LOCKABLE
173	___unlock_dcache_all a2 a3
174#endif
175
176#if XCHAL_ICACHE_LINE_LOCKABLE
177	___unlock_icache_all a2 a3
178#endif
179
180	___invalidate_dcache_all a2 a3
181	___invalidate_icache_all a2 a3
182
183	isync
184
185	/* Unpack data sections
186	 *
187	 * The linker script used to build the Linux kernel image
188	 * creates a table located at __boot_reloc_table_start
189	 * that contans the information what data needs to be unpacked.
190	 *
191	 * Uses a2-a7.
192	 */
193
194	movi	a2, __boot_reloc_table_start
195	movi	a3, __boot_reloc_table_end
196
1971:	beq	a2, a3, 3f	# no more entries?
198	l32i	a4, a2, 0	# start destination (in RAM)
199	l32i	a5, a2, 4	# end desination (in RAM)
200	l32i	a6, a2, 8	# start source (in ROM)
201	addi	a2, a2, 12	# next entry
202	beq	a4, a5, 1b	# skip, empty entry
203	beq	a4, a6, 1b	# skip, source and dest. are the same
204
2052:	l32i	a7, a6, 0	# load word
206	addi	a6, a6, 4
207	s32i	a7, a4, 0	# store word
208	addi	a4, a4, 4
209	bltu	a4, a5, 2b
210	j	1b
211
2123:
213	/* All code and initialized data segments have been copied.
214	 * Now clear the BSS segment.
215	 */
216
217	movi	a2, __bss_start	# start of BSS
218	movi	a3, __bss_stop	# end of BSS
219
220	__loopt	a2, a3, a4, 2
221	s32i	a0, a2, 0
222	__endla	a2, a4, 4
223
224#if XCHAL_DCACHE_IS_WRITEBACK
225
226	/* After unpacking, flush the writeback cache to memory so the
227	 * instructions/data are available.
228	 */
229
230	___flush_dcache_all a2 a3
231#endif
232	memw
233	isync
234	___invalidate_icache_all a2 a3
235	isync
236
237	/* Setup stack and enable window exceptions (keep irqs disabled) */
238
239	movi	a1, init_thread_union
240	addi	a1, a1, KERNEL_STACK_SIZE
241
242	movi	a2, (1 << PS_WOE_BIT) | LOCKLEVEL
243					# WOE=1, INTLEVEL=LOCKLEVEL, UM=0
244	wsr	a2, ps			# (enable reg-windows; progmode stack)
245	rsync
246
247	/* Set up EXCSAVE[DEBUGLEVEL] to point to the Debug Exception Handler.*/
248
249	movi	a2, debug_exception
250	wsr	a2, SREG_EXCSAVE + XCHAL_DEBUGLEVEL
251
252	/* Set up EXCSAVE[1] to point to the exc_table. */
253
254	movi	a6, exc_table
255	xsr	a6, excsave1
256
257	/* init_arch kick-starts the linux kernel */
258
259	movi	a4, init_arch
260	callx4	a4
261
262	movi	a4, start_kernel
263	callx4	a4
264
265should_never_return:
266	j	should_never_return
267
268ENDPROC(_startup)
269
270/*
271 * BSS section
272 */
273
274__PAGE_ALIGNED_BSS
275#ifdef CONFIG_MMU
276ENTRY(swapper_pg_dir)
277	.fill	PAGE_SIZE, 1, 0
278END(swapper_pg_dir)
279#endif
280ENTRY(empty_zero_page)
281	.fill	PAGE_SIZE, 1, 0
282END(empty_zero_page)
283