xref: /openbmc/linux/arch/xtensa/kernel/head.S (revision 2891f2d5) 
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.Lstartup:
63	.word	_startup
64
65	.align	4
66_SetupOCD:
67	/*
68	 * Initialize WB, WS, and clear PS.EXCM (to allow loop instructions).
69	 * Set Interrupt Level just below XCHAL_DEBUGLEVEL to allow
70	 * xt-gdb to single step via DEBUG exceptions received directly
71	 * by ocd.
72	 */
73	movi	a1, 1
74	movi	a0, 0
75	wsr	a1, windowstart
76	wsr	a0, windowbase
77	rsync
78
79	movi	a1, LOCKLEVEL
80	wsr	a1, ps
81	rsync
82
83	.global _SetupMMU
84_SetupMMU:
85	Offset = _SetupMMU - _start
86
87#ifdef CONFIG_INITIALIZE_XTENSA_MMU_INSIDE_VMLINUX
88	initialize_mmu
89#if defined(CONFIG_MMU) && XCHAL_HAVE_PTP_MMU && XCHAL_HAVE_SPANNING_WAY
90	rsr	a2, excsave1
91	movi	a3, 0x08000000
92	bgeu	a2, a3, 1f
93	movi	a3, 0xd0000000
94	add	a2, a2, a3
95	wsr	a2, excsave1
961:
97#endif
98#endif
99	.end	no-absolute-literals
100
101	l32r	a0, .Lstartup
102	jx	a0
103
104ENDPROC(_start)
105
106	__REF
107	.literal_position
108
109ENTRY(_startup)
110
111	/* Set a0 to 0 for the remaining initialization. */
112
113	movi	a0, 0
114
115#if XCHAL_HAVE_VECBASE
116	movi    a2, VECBASE_VADDR
117	wsr	a2, vecbase
118#endif
119
120	/* Clear debugging registers. */
121
122#if XCHAL_HAVE_DEBUG
123#if XCHAL_NUM_IBREAK > 0
124	wsr	a0, ibreakenable
125#endif
126	wsr	a0, icount
127	movi	a1, 15
128	wsr	a0, icountlevel
129
130	.set	_index, 0
131	.rept	XCHAL_NUM_DBREAK
132	wsr	a0, SREG_DBREAKC + _index
133	.set	_index, _index + 1
134	.endr
135#endif
136
137	/* Clear CCOUNT (not really necessary, but nice) */
138
139	wsr	a0, ccount	# not really necessary, but nice
140
141	/* Disable zero-loops. */
142
143#if XCHAL_HAVE_LOOPS
144	wsr	a0, lcount
145#endif
146
147	/* Disable all timers. */
148
149	.set	_index, 0
150	.rept	XCHAL_NUM_TIMERS
151	wsr	a0, SREG_CCOMPARE + _index
152	.set	_index, _index + 1
153	.endr
154
155	/* Interrupt initialization. */
156
157	movi	a2, XCHAL_INTTYPE_MASK_SOFTWARE | XCHAL_INTTYPE_MASK_EXTERN_EDGE
158	wsr	a0, intenable
159	wsr	a2, intclear
160
161	/* Disable coprocessors. */
162
163#if XCHAL_HAVE_CP
164	wsr	a0, cpenable
165#endif
166
167	/*  Initialize the caches.
168	 *  a2, a3 are just working registers (clobbered).
169	 */
170
171#if XCHAL_DCACHE_LINE_LOCKABLE
172	___unlock_dcache_all a2 a3
173#endif
174
175#if XCHAL_ICACHE_LINE_LOCKABLE
176	___unlock_icache_all a2 a3
177#endif
178
179	___invalidate_dcache_all a2 a3
180	___invalidate_icache_all a2 a3
181
182	isync
183
184#ifdef CONFIG_HAVE_SMP
185	movi	a2, CCON	# MX External Register to Configure Cache
186	movi	a3, 1
187	wer	a3, a2
188#endif
189
190	/* Setup stack and enable window exceptions (keep irqs disabled) */
191
192	movi	a1, start_info
193	l32i	a1, a1, 0
194
195	movi	a2, (1 << PS_WOE_BIT) | LOCKLEVEL
196					# WOE=1, INTLEVEL=LOCKLEVEL, UM=0
197	wsr	a2, ps			# (enable reg-windows; progmode stack)
198	rsync
199
200#ifdef CONFIG_SMP
201	/*
202	 * Notice that we assume with SMP that cores have PRID
203	 * supported by the cores.
204	 */
205	rsr	a2, prid
206	bnez	a2, .Lboot_secondary
207
208#endif  /* CONFIG_SMP */
209
210	/* Unpack data sections
211	 *
212	 * The linker script used to build the Linux kernel image
213	 * creates a table located at __boot_reloc_table_start
214	 * that contans the information what data needs to be unpacked.
215	 *
216	 * Uses a2-a7.
217	 */
218
219	movi	a2, __boot_reloc_table_start
220	movi	a3, __boot_reloc_table_end
221
2221:	beq	a2, a3, 3f	# no more entries?
223	l32i	a4, a2, 0	# start destination (in RAM)
224	l32i	a5, a2, 4	# end desination (in RAM)
225	l32i	a6, a2, 8	# start source (in ROM)
226	addi	a2, a2, 12	# next entry
227	beq	a4, a5, 1b	# skip, empty entry
228	beq	a4, a6, 1b	# skip, source and dest. are the same
229
2302:	l32i	a7, a6, 0	# load word
231	addi	a6, a6, 4
232	s32i	a7, a4, 0	# store word
233	addi	a4, a4, 4
234	bltu	a4, a5, 2b
235	j	1b
236
2373:
238	/* All code and initialized data segments have been copied.
239	 * Now clear the BSS segment.
240	 */
241
242	movi	a2, __bss_start	# start of BSS
243	movi	a3, __bss_stop	# end of BSS
244
245	__loopt	a2, a3, a4, 2
246	s32i	a0, a2, 0
247	__endla	a2, a3, 4
248
249#if XCHAL_DCACHE_IS_WRITEBACK
250
251	/* After unpacking, flush the writeback cache to memory so the
252	 * instructions/data are available.
253	 */
254
255	___flush_dcache_all a2 a3
256#endif
257	memw
258	isync
259	___invalidate_icache_all a2 a3
260	isync
261
262	movi	a6, 0
263	xsr	a6, excsave1
264
265	/* init_arch kick-starts the linux kernel */
266
267	movi	a4, init_arch
268	callx4	a4
269
270	movi	a4, start_kernel
271	callx4	a4
272
273should_never_return:
274	j	should_never_return
275
276#ifdef CONFIG_SMP
277.Lboot_secondary:
278
279	movi	a2, cpu_start_ccount
2801:
281	l32i	a3, a2, 0
282	beqi	a3, 0, 1b
283	movi	a3, 0
284	s32i	a3, a2, 0
285	memw
2861:
287	l32i	a3, a2, 0
288	beqi	a3, 0, 1b
289	wsr	a3, ccount
290	movi	a3, 0
291	s32i	a3, a2, 0
292	memw
293
294	movi	a6, 0
295	wsr	a6, excsave1
296
297	movi	a4, secondary_start_kernel
298	callx4	a4
299	j	should_never_return
300
301#endif  /* CONFIG_SMP */
302
303ENDPROC(_startup)
304
305#ifdef CONFIG_HOTPLUG_CPU
306
307ENTRY(cpu_restart)
308
309#if XCHAL_DCACHE_IS_WRITEBACK
310	___flush_invalidate_dcache_all a2 a3
311#else
312	___invalidate_dcache_all a2 a3
313#endif
314	memw
315	movi	a2, CCON	# MX External Register to Configure Cache
316	movi	a3, 0
317	wer	a3, a2
318	extw
319
320	rsr	a0, prid
321	neg	a2, a0
322	movi	a3, cpu_start_id
323	s32i	a2, a3, 0
324#if XCHAL_DCACHE_IS_WRITEBACK
325	dhwbi	a3, 0
326#endif
3271:
328	l32i	a2, a3, 0
329	dhi	a3, 0
330	bne	a2, a0, 1b
331
332	/*
333	 * Initialize WB, WS, and clear PS.EXCM (to allow loop instructions).
334	 * Set Interrupt Level just below XCHAL_DEBUGLEVEL to allow
335	 * xt-gdb to single step via DEBUG exceptions received directly
336	 * by ocd.
337	 */
338	movi	a1, 1
339	movi	a0, 0
340	wsr	a1, windowstart
341	wsr	a0, windowbase
342	rsync
343
344	movi	a1, LOCKLEVEL
345	wsr	a1, ps
346	rsync
347
348	j	_startup
349
350ENDPROC(cpu_restart)
351
352#endif  /* CONFIG_HOTPLUG_CPU */
353
354/*
355 * DATA section
356 */
357
358        .section ".data.init.refok"
359        .align  4
360ENTRY(start_info)
361        .long   init_thread_union + KERNEL_STACK_SIZE
362
363/*
364 * BSS section
365 */
366
367__PAGE_ALIGNED_BSS
368#ifdef CONFIG_MMU
369ENTRY(swapper_pg_dir)
370	.fill	PAGE_SIZE, 1, 0
371END(swapper_pg_dir)
372#endif
373ENTRY(empty_zero_page)
374	.fill	PAGE_SIZE, 1, 0
375END(empty_zero_page)
376