xref: /openbmc/linux/arch/xtensa/kernel/head.S (revision 79e790ff) 
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#include <asm/mxregs.h>
23
24#include <linux/init.h>
25#include <linux/linkage.h>
26
27/*
28 * This module contains the entry code for kernel images. It performs the
29 * minimal setup needed to call the generic C routines.
30 *
31 * Prerequisites:
32 *
33 * - The kernel image has been loaded to the actual address where it was
34 *   compiled to.
35 * - a2 contains either 0 or a pointer to a list of boot parameters.
36 *   (see setup.c for more details)
37 *
38 */
39
40/*
41 *  _start
42 *
43 *  The bootloader passes a pointer to a list of boot parameters in a2.
44 */
45
46	/* The first bytes of the kernel image must be an instruction, so we
47	 * manually allocate and define the literal constant we need for a jx
48	 * instruction.
49	 */
50
51	__HEAD
52	.begin	no-absolute-literals
53
54ENTRY(_start)
55
56	/* Preserve the pointer to the boot parameter list in EXCSAVE_1 */
57	wsr     a2, excsave1
58	_j	_SetupOCD
59
60	.align	4
61	.literal_position
62_SetupOCD:
63	/*
64	 * Initialize WB, WS, and clear PS.EXCM (to allow loop instructions).
65	 * Set Interrupt Level just below XCHAL_DEBUGLEVEL to allow
66	 * xt-gdb to single step via DEBUG exceptions received directly
67	 * by ocd.
68	 */
69	movi	a1, 1
70	movi	a0, 0
71	wsr	a1, windowstart
72	wsr	a0, windowbase
73	rsync
74
75	movi	a1, LOCKLEVEL
76	wsr	a1, ps
77	rsync
78
79	.global _SetupMMU
80_SetupMMU:
81	Offset = _SetupMMU - _start
82
83#ifdef CONFIG_INITIALIZE_XTENSA_MMU_INSIDE_VMLINUX
84	initialize_mmu
85#if defined(CONFIG_MMU) && XCHAL_HAVE_PTP_MMU && XCHAL_HAVE_SPANNING_WAY
86	rsr	a2, excsave1
87	movi	a3, XCHAL_KSEG_PADDR
88	bltu	a2, a3, 1f
89	sub	a2, a2, a3
90	movi	a3, XCHAL_KSEG_SIZE
91	bgeu	a2, a3, 1f
92	movi	a3, XCHAL_KSEG_CACHED_VADDR
93	add	a2, a2, a3
94	wsr	a2, excsave1
951:
96#endif
97#endif
98
99	movi	a0, _startup
100	jx	a0
101
102ENDPROC(_start)
103	.end	no-absolute-literals
104
105	__REF
106	.literal_position
107
108ENTRY(_startup)
109
110	/* Set a0 to 0 for the remaining initialization. */
111
112	movi	a0, 0
113
114#if XCHAL_HAVE_VECBASE
115	movi    a2, VECBASE_VADDR
116	wsr	a2, vecbase
117#endif
118
119	/* Clear debugging registers. */
120
121#if XCHAL_HAVE_DEBUG
122#if XCHAL_NUM_IBREAK > 0
123	wsr	a0, ibreakenable
124#endif
125	wsr	a0, icount
126	movi	a1, 15
127	wsr	a0, icountlevel
128
129	.set	_index, 0
130	.rept	XCHAL_NUM_DBREAK
131	wsr	a0, SREG_DBREAKC + _index
132	.set	_index, _index + 1
133	.endr
134#endif
135
136	/* Clear CCOUNT (not really necessary, but nice) */
137
138	wsr	a0, ccount	# not really necessary, but nice
139
140	/* Disable zero-loops. */
141
142#if XCHAL_HAVE_LOOPS
143	wsr	a0, lcount
144#endif
145
146	/* Disable all timers. */
147
148	.set	_index, 0
149	.rept	XCHAL_NUM_TIMERS
150	wsr	a0, SREG_CCOMPARE + _index
151	.set	_index, _index + 1
152	.endr
153
154	/* Interrupt initialization. */
155
156	movi	a2, XCHAL_INTTYPE_MASK_SOFTWARE | XCHAL_INTTYPE_MASK_EXTERN_EDGE
157	wsr	a0, intenable
158	wsr	a2, intclear
159
160	/* Disable coprocessors. */
161
162#if XCHAL_HAVE_CP
163	wsr	a0, cpenable
164#endif
165
166	/*  Initialize the caches.
167	 *  a2, a3 are just working registers (clobbered).
168	 */
169
170#if XCHAL_DCACHE_LINE_LOCKABLE
171	___unlock_dcache_all a2 a3
172#endif
173
174#if XCHAL_ICACHE_LINE_LOCKABLE
175	___unlock_icache_all a2 a3
176#endif
177
178	___invalidate_dcache_all a2 a3
179	___invalidate_icache_all a2 a3
180
181	isync
182
183	initialize_cacheattr
184
185#ifdef CONFIG_HAVE_SMP
186	movi	a2, CCON	# MX External Register to Configure Cache
187	movi	a3, 1
188	wer	a3, a2
189#endif
190
191	/* Setup stack and enable window exceptions (keep irqs disabled) */
192
193	movi	a1, start_info
194	l32i	a1, a1, 0
195
196	movi	a2, PS_WOE_MASK | LOCKLEVEL
197					# WOE=1, INTLEVEL=LOCKLEVEL, UM=0
198	wsr	a2, ps			# (enable reg-windows; progmode stack)
199	rsync
200
201#ifdef CONFIG_SMP
202	/*
203	 * Notice that we assume with SMP that cores have PRID
204	 * supported by the cores.
205	 */
206	rsr	a2, prid
207	bnez	a2, .Lboot_secondary
208
209#endif  /* CONFIG_SMP */
210
211	/* Unpack data sections
212	 *
213	 * The linker script used to build the Linux kernel image
214	 * creates a table located at __boot_reloc_table_start
215	 * that contains the information what data needs to be unpacked.
216	 *
217	 * Uses a2-a7.
218	 */
219
220	movi	a2, __boot_reloc_table_start
221	movi	a3, __boot_reloc_table_end
222
2231:	beq	a2, a3, 3f	# no more entries?
224	l32i	a4, a2, 0	# start destination (in RAM)
225	l32i	a5, a2, 4	# end destination (in RAM)
226	l32i	a6, a2, 8	# start source (in ROM)
227	addi	a2, a2, 12	# next entry
228	beq	a4, a5, 1b	# skip, empty entry
229	beq	a4, a6, 1b	# skip, source and dest. are the same
230
2312:	l32i	a7, a6, 0	# load word
232	addi	a6, a6, 4
233	s32i	a7, a4, 0	# store word
234	addi	a4, a4, 4
235	bltu	a4, a5, 2b
236	j	1b
237
2383:
239	/* All code and initialized data segments have been copied.
240	 * Now clear the BSS segment.
241	 */
242
243	movi	a2, __bss_start	# start of BSS
244	movi	a3, __bss_stop	# end of BSS
245
246	__loopt	a2, a3, a4, 2
247	s32i	a0, a2, 0
248	__endla	a2, a3, 4
249
250#if XCHAL_DCACHE_IS_WRITEBACK
251
252	/* After unpacking, flush the writeback cache to memory so the
253	 * instructions/data are available.
254	 */
255
256	___flush_dcache_all a2 a3
257#endif
258	memw
259	isync
260	___invalidate_icache_all a2 a3
261	isync
262
263#ifdef CONFIG_XIP_KERNEL
264	/* Setup bootstrap CPU stack in XIP kernel */
265
266	movi	a1, start_info
267	l32i	a1, a1, 0
268#endif
269
270	movi	a6, 0
271	xsr	a6, excsave1
272
273	/* init_arch kick-starts the linux kernel */
274
275	call4	init_arch
276	call4	start_kernel
277
278should_never_return:
279	j	should_never_return
280
281#ifdef CONFIG_SMP
282.Lboot_secondary:
283
284	movi	a2, cpu_start_ccount
2851:
286	memw
287	l32i	a3, a2, 0
288	beqi	a3, 0, 1b
289	movi	a3, 0
290	s32i	a3, a2, 0
2911:
292	memw
293	l32i	a3, a2, 0
294	beqi	a3, 0, 1b
295	wsr	a3, ccount
296	movi	a3, 0
297	s32i	a3, a2, 0
298	memw
299
300	movi	a6, 0
301	wsr	a6, excsave1
302
303	call4	secondary_start_kernel
304	j	should_never_return
305
306#endif  /* CONFIG_SMP */
307
308ENDPROC(_startup)
309
310#ifdef CONFIG_HOTPLUG_CPU
311
312ENTRY(cpu_restart)
313
314#if XCHAL_DCACHE_IS_WRITEBACK
315	___flush_invalidate_dcache_all a2 a3
316#else
317	___invalidate_dcache_all a2 a3
318#endif
319	memw
320	movi	a2, CCON	# MX External Register to Configure Cache
321	movi	a3, 0
322	wer	a3, a2
323	extw
324
325	rsr	a0, prid
326	neg	a2, a0
327	movi	a3, cpu_start_id
328	memw
329	s32i	a2, a3, 0
330#if XCHAL_DCACHE_IS_WRITEBACK
331	dhwbi	a3, 0
332#endif
3331:
334	memw
335	l32i	a2, a3, 0
336	dhi	a3, 0
337	bne	a2, a0, 1b
338
339	/*
340	 * Initialize WB, WS, and clear PS.EXCM (to allow loop instructions).
341	 * Set Interrupt Level just below XCHAL_DEBUGLEVEL to allow
342	 * xt-gdb to single step via DEBUG exceptions received directly
343	 * by ocd.
344	 */
345	movi	a1, 1
346	movi	a0, 0
347	wsr	a1, windowstart
348	wsr	a0, windowbase
349	rsync
350
351	movi	a1, LOCKLEVEL
352	wsr	a1, ps
353	rsync
354
355	j	_startup
356
357ENDPROC(cpu_restart)
358
359#endif  /* CONFIG_HOTPLUG_CPU */
360
361/*
362 * DATA section
363 */
364
365	__REFDATA
366	.align  4
367ENTRY(start_info)
368	.long	init_thread_union + KERNEL_STACK_SIZE
369
370/*
371 * BSS section
372 */
373
374__PAGE_ALIGNED_BSS
375#ifdef CONFIG_MMU
376ENTRY(swapper_pg_dir)
377	.fill	PAGE_SIZE, 1, 0
378END(swapper_pg_dir)
379#endif
380ENTRY(empty_zero_page)
381	.fill	PAGE_SIZE, 1, 0
382END(empty_zero_page)
383