xref: /openbmc/linux/arch/xtensa/kernel/head.S (revision 827634ad) 
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_RESET_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 - 1
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	/* Set up EXCSAVE[DEBUGLEVEL] to point to the Debug Exception Handler.*/
201
202	movi	a2, debug_exception
203	wsr	a2, SREG_EXCSAVE + XCHAL_DEBUGLEVEL
204
205#ifdef CONFIG_SMP
206	/*
207	 * Notice that we assume with SMP that cores have PRID
208	 * supported by the cores.
209	 */
210	rsr	a2, prid
211	bnez	a2, .Lboot_secondary
212
213#endif  /* CONFIG_SMP */
214
215	/* Unpack data sections
216	 *
217	 * The linker script used to build the Linux kernel image
218	 * creates a table located at __boot_reloc_table_start
219	 * that contans the information what data needs to be unpacked.
220	 *
221	 * Uses a2-a7.
222	 */
223
224	movi	a2, __boot_reloc_table_start
225	movi	a3, __boot_reloc_table_end
226
2271:	beq	a2, a3, 3f	# no more entries?
228	l32i	a4, a2, 0	# start destination (in RAM)
229	l32i	a5, a2, 4	# end desination (in RAM)
230	l32i	a6, a2, 8	# start source (in ROM)
231	addi	a2, a2, 12	# next entry
232	beq	a4, a5, 1b	# skip, empty entry
233	beq	a4, a6, 1b	# skip, source and dest. are the same
234
2352:	l32i	a7, a6, 0	# load word
236	addi	a6, a6, 4
237	s32i	a7, a4, 0	# store word
238	addi	a4, a4, 4
239	bltu	a4, a5, 2b
240	j	1b
241
2423:
243	/* All code and initialized data segments have been copied.
244	 * Now clear the BSS segment.
245	 */
246
247	movi	a2, __bss_start	# start of BSS
248	movi	a3, __bss_stop	# end of BSS
249
250	__loopt	a2, a3, a4, 2
251	s32i	a0, a2, 0
252	__endla	a2, a4, 4
253
254#if XCHAL_DCACHE_IS_WRITEBACK
255
256	/* After unpacking, flush the writeback cache to memory so the
257	 * instructions/data are available.
258	 */
259
260	___flush_dcache_all a2 a3
261#endif
262	memw
263	isync
264	___invalidate_icache_all a2 a3
265	isync
266
267	movi	a6, 0
268	xsr	a6, excsave1
269
270	/* init_arch kick-starts the linux kernel */
271
272	movi	a4, init_arch
273	callx4	a4
274
275	movi	a4, start_kernel
276	callx4	a4
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	l32i	a3, a2, 0
287	beqi	a3, 0, 1b
288	movi	a3, 0
289	s32i	a3, a2, 0
290	memw
2911:
292	l32i	a3, a2, 0
293	beqi	a3, 0, 1b
294	wsr	a3, ccount
295	movi	a3, 0
296	s32i	a3, a2, 0
297	memw
298
299	movi	a6, 0
300	wsr	a6, excsave1
301
302	movi	a4, secondary_start_kernel
303	callx4	a4
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	s32i	a2, a3, 0
329#if XCHAL_DCACHE_IS_WRITEBACK
330	dhwbi	a3, 0
331#endif
3321:
333	l32i	a2, a3, 0
334	dhi	a3, 0
335	bne	a2, a0, 1b
336
337	/*
338	 * Initialize WB, WS, and clear PS.EXCM (to allow loop instructions).
339	 * Set Interrupt Level just below XCHAL_DEBUGLEVEL to allow
340	 * xt-gdb to single step via DEBUG exceptions received directly
341	 * by ocd.
342	 */
343	movi	a1, 1
344	movi	a0, 0
345	wsr	a1, windowstart
346	wsr	a0, windowbase
347	rsync
348
349	movi	a1, LOCKLEVEL
350	wsr	a1, ps
351	rsync
352
353	j	_startup
354
355ENDPROC(cpu_restart)
356
357#endif  /* CONFIG_HOTPLUG_CPU */
358
359/*
360 * DATA section
361 */
362
363        .section ".data.init.refok"
364        .align  4
365ENTRY(start_info)
366        .long   init_thread_union + KERNEL_STACK_SIZE
367
368/*
369 * BSS section
370 */
371
372__PAGE_ALIGNED_BSS
373#ifdef CONFIG_MMU
374ENTRY(swapper_pg_dir)
375	.fill	PAGE_SIZE, 1, 0
376END(swapper_pg_dir)
377#endif
378ENTRY(empty_zero_page)
379	.fill	PAGE_SIZE, 1, 0
380END(empty_zero_page)
381