/* * arch/xtensa/kernel/head.S * * Xtensa Processor startup code. * * This file is subject to the terms and conditions of the GNU General Public * License. See the file "COPYING" in the main directory of this archive * for more details. * * Copyright (C) 2001 - 2005 Tensilica Inc. * * Chris Zankel * Marc Gauthier * Joe Taylor * Kevin Chea */ #include #include #include #include /* * This module contains the entry code for kernel images. It performs the * minimal setup needed to call the generic C routines. * * Prerequisites: * * - The kernel image has been loaded to the actual address where it was * compiled to. * - a2 contains either 0 or a pointer to a list of boot parameters. * (see setup.c for more details) * */ .macro iterate from, to , cmd .ifeq ((\to - \from) & ~0xfff) \cmd \from iterate "(\from+1)", \to, \cmd .endif .endm /* * _start * * The bootloader passes a pointer to a list of boot parameters in a2. */ /* The first bytes of the kernel image must be an instruction, so we * manually allocate and define the literal constant we need for a jx * instruction. */ .section .head.text, "ax" .globl _start _start: _j 2f .align 4 1: .word _startup 2: l32r a0, 1b jx a0 .text .align 4 _startup: /* Disable interrupts and exceptions. */ movi a0, XCHAL_PS_EXCM_MASK wsr a0, PS /* Preserve the pointer to the boot parameter list in EXCSAVE_1 */ wsr a2, EXCSAVE_1 /* Start with a fresh windowbase and windowstart. */ movi a1, 1 movi a0, 0 wsr a1, WINDOWSTART wsr a0, WINDOWBASE rsync /* Set a0 to 0 for the remaining initialization. */ movi a0, 0 /* Clear debugging registers. */ #if XCHAL_HAVE_DEBUG wsr a0, IBREAKENABLE wsr a0, ICOUNT movi a1, 15 wsr a0, ICOUNTLEVEL .macro reset_dbreak num wsr a0, DBREAKC + \num .endm iterate 0, XCHAL_NUM_IBREAK-1, reset_dbreak #endif /* Clear CCOUNT (not really necessary, but nice) */ wsr a0, CCOUNT # not really necessary, but nice /* Disable zero-loops. */ #if XCHAL_HAVE_LOOPS wsr a0, LCOUNT #endif /* Disable all timers. */ .macro reset_timer num wsr a0, CCOMPARE_0 + \num .endm iterate 0, XCHAL_NUM_TIMERS-1, reset_timer /* Interrupt initialization. */ movi a2, XCHAL_INTTYPE_MASK_SOFTWARE | XCHAL_INTTYPE_MASK_EXTERN_EDGE wsr a0, INTENABLE wsr a2, INTCLEAR /* Disable coprocessors. */ #if XCHAL_CP_NUM > 0 wsr a0, CPENABLE #endif /* Set PS.INTLEVEL=1, PS.WOE=0, kernel stack, PS.EXCM=0 * * Note: PS.EXCM must be cleared before using any loop * instructions; otherwise, they are silently disabled, and * at most one iteration of the loop is executed. */ movi a1, 1 wsr a1, PS rsync /* Initialize the caches. * Does not include flushing writeback d-cache. * a6, a7 are just working registers (clobbered). */ icache_reset a2, a3 dcache_reset a2, a3 /* Unpack data sections * * The linker script used to build the Linux kernel image * creates a table located at __boot_reloc_table_start * that contans the information what data needs to be unpacked. * * Uses a2-a7. */ movi a2, __boot_reloc_table_start movi a3, __boot_reloc_table_end 1: beq a2, a3, 3f # no more entries? l32i a4, a2, 0 # start destination (in RAM) l32i a5, a2, 4 # end desination (in RAM) l32i a6, a2, 8 # start source (in ROM) addi a2, a2, 12 # next entry beq a4, a5, 1b # skip, empty entry beq a4, a6, 1b # skip, source and dest. are the same 2: l32i a7, a6, 0 # load word addi a6, a6, 4 s32i a7, a4, 0 # store word addi a4, a4, 4 bltu a4, a5, 2b j 1b 3: /* All code and initialized data segments have been copied. * Now clear the BSS segment. */ movi a2, _bss_start # start of BSS movi a3, _bss_end # end of BSS 1: addi a2, a2, 4 s32i a0, a2, 0 blt a2, a3, 1b #if XCHAL_DCACHE_IS_WRITEBACK /* After unpacking, flush the writeback cache to memory so the * instructions/data are available. */ dcache_writeback_all a2, a3 #endif /* Setup stack and enable window exceptions (keep irqs disabled) */ movi a1, init_thread_union addi a1, a1, KERNEL_STACK_SIZE movi a2, 0x00040001 # WOE=1, INTLEVEL=1, UM=0 wsr a2, PS # (enable reg-windows; progmode stack) rsync /* Set up EXCSAVE[DEBUGLEVEL] to point to the Debug Exception Handler.*/ movi a2, debug_exception wsr a2, EXCSAVE + XCHAL_DEBUGLEVEL /* Set up EXCSAVE[1] to point to the exc_table. */ movi a6, exc_table xsr a6, EXCSAVE_1 /* init_arch kick-starts the linux kernel */ movi a4, init_arch callx4 a4 movi a4, start_kernel callx4 a4 should_never_return: j should_never_return /* Define some common data structures here. We define them * here in this assembly file due to their unusual alignment * requirements. */ .comm swapper_pg_dir,PAGE_SIZE,PAGE_SIZE .comm empty_bad_page_table,PAGE_SIZE,PAGE_SIZE .comm empty_bad_page,PAGE_SIZE,PAGE_SIZE .comm empty_zero_page,PAGE_SIZE,PAGE_SIZE