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