arch/xtensa/kernel/head.S

   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
  53 ENTRY(_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
  78 1:
  79 #endif
  80 #endif
  81         .end    no-absolute-literals
  82
  83         l32r    a0, .Lstartup
  84         jx      a0
  85
  86 ENDPROC(_start)
  87
  88         __INIT
  89         .literal_position
  90
  91 ENTRY(_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
 197 1:      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
 205 2:      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
 212 3:
 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
 265 should_never_return:
 266         j       should_never_return
 267
 268 ENDPROC(_startup)
 269
 270 /*
 271  * BSS section
 272  */
 273
 274 __PAGE_ALIGNED_BSS
 275 #ifdef CONFIG_MMU
 276 ENTRY(swapper_pg_dir)
 277         .fill   PAGE_SIZE, 1, 0
 278 END(swapper_pg_dir)
 279 #endif
 280 ENTRY(empty_zero_page)
 281         .fill   PAGE_SIZE, 1, 0
 282 END(empty_zero_page)