#
# Copyright (c) 2003-2004 Jakub Jermar
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#
# - Redistributions of source code must retain the above copyright
#   notice, this list of conditions and the following disclaimer.
# - Redistributions in binary form must reproduce the above copyright
#   notice, this list of conditions and the following disclaimer in the
#   documentation and/or other materials provided with the distribution.
# - The name of the author may not be used to endorse or promote products
#   derived from this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
# OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
# IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
# NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
# THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#

#include <arch/asm/regname.h>
#include <arch/mm/page.h>
#include <arch/asm/boot.h>
#include <arch/context_offset.h>
#include <arch/stack.h>

.text

.set noat
.set noreorder
.set nomacro

.global kernel_image_start
.global tlb_refill_entry
.global cache_error_entry
.global exception_entry
.global userspace_asm

# Which status bits should are thread-local
#define REG_SAVE_MASK 0x1f # KSU(UM), EXL, ERL, IE

# Save registers to space defined by \r
# We will change status: Disable ERL, EXL, UM, IE
# These changes will be automatically reversed in REGISTER_LOAD
# %sp is NOT saved as part of these registers
.macro REGISTERS_STORE_AND_EXC_RESET r
	sw $at, EOFFSET_AT(\r)
	sw $v0, EOFFSET_V0(\r)
	sw $v1, EOFFSET_V1(\r)
	sw $a0, EOFFSET_A0(\r)
	sw $a1, EOFFSET_A1(\r)
	sw $a2, EOFFSET_A2(\r)
	sw $a3, EOFFSET_A3(\r)
	sw $t0, EOFFSET_T0(\r)
	sw $t1, EOFFSET_T1(\r)
	sw $t2, EOFFSET_T2(\r)
	sw $t3, EOFFSET_T3(\r)
	sw $t4, EOFFSET_T4(\r)
	sw $t5, EOFFSET_T5(\r)
	sw $t6, EOFFSET_T6(\r)
	sw $t7, EOFFSET_T7(\r)
	sw $t8, EOFFSET_T8(\r)
	sw $t9, EOFFSET_T9(\r)
	
	mflo $at
	sw $at, EOFFSET_LO(\r)
	mfhi $at
	sw $at, EOFFSET_HI(\r)
	
	sw $gp, EOFFSET_GP(\r)
	sw $ra, EOFFSET_RA(\r)
	sw $k1, EOFFSET_K1(\r)
	
	mfc0 $t0, $status
	mfc0 $t1, $epc
	
	# save only KSU, EXL, ERL, IE
	and $t2, $t0, REG_SAVE_MASK
	
	# clear KSU, EXL, ERL, IE
	li $t3, ~(REG_SAVE_MASK)
	and $t0, $t0, $t3
	
	sw $t2, EOFFSET_STATUS(\r)
	sw $t1, EOFFSET_EPC(\r)
	mtc0 $t0, $status
.endm

.macro REGISTERS_LOAD r
	# Update only UM, EXR, IE from status, the rest
	# is controlled by OS and not bound to task
	mfc0 $t0, $status
	lw $t1,EOFFSET_STATUS(\r)
	
	# Mask UM, EXL, ERL, IE
	li $t2, ~REG_SAVE_MASK
	and $t0, $t0, $t2
	
	# Copy UM, EXL, ERL, IE from saved status
	or $t0, $t0, $t1
	mtc0 $t0, $status
	
	lw $v0, EOFFSET_V0(\r)
	lw $v1, EOFFSET_V1(\r)
	lw $a0, EOFFSET_A0(\r)
	lw $a1, EOFFSET_A1(\r)
	lw $a2, EOFFSET_A2(\r)
	lw $a3, EOFFSET_A3(\r)
	lw $t0, EOFFSET_T0(\r)
	lw $t1, EOFFSET_T1(\r)
	lw $t2, EOFFSET_T2(\r)
	lw $t3, EOFFSET_T3(\r)
	lw $t4, EOFFSET_T4(\r)
	lw $t5, EOFFSET_T5(\r)
	lw $t6, EOFFSET_T6(\r)
	lw $t7, EOFFSET_T7(\r)
	lw $t8, EOFFSET_T8(\r)
	lw $t9, EOFFSET_T9(\r)
	
	lw $gp, EOFFSET_GP(\r)
	lw $ra, EOFFSET_RA(\r)
	lw $k1, EOFFSET_K1(\r)
	
	lw $at, EOFFSET_LO(\r)
	mtlo $at
	lw $at, EOFFSET_HI(\r)
	mthi $at
	
	lw $at, EOFFSET_EPC(\r)
	mtc0 $at, $epc
	
	lw $at, EOFFSET_AT(\r)
	lw $sp, EOFFSET_SP(\r)
.endm

# Move kernel stack pointer address to register K0
# - if we are in user mode, load the appropriate stack address
.macro KERNEL_STACK_TO_K0
	# if we are in user mode
	mfc0 $k0, $status
	andi $k0, 0x10
	
	beq $k0, $0, 1f
	add $k0, $sp, 0
	
	# move $k0 pointer to kernel stack
	lui $k0, %hi(supervisor_sp)
	ori $k0, $k0, %lo(supervisor_sp)
	
	# move $k0 (supervisor_sp)
	lw $k0, 0($k0)
	
	1:
.endm

.org 0x0
kernel_image_start:
	# load temporary stack
	lui $sp, %hi(end_stack)
	ori $sp, $sp, %lo(end_stack)
	
	# Not sure about this, but might
	# be needed for PIC code
	lui $gp, 0x8000
	
	# $a1 contains physical address of bootinfo_t
	jal arch_pre_main
	nop
	
	j main_bsp
	nop

.space TEMP_STACK_SIZE
end_stack:

tlb_refill_entry:
	j tlb_refill_handler
	nop

cache_error_entry:
	j cache_error_handler
	nop

exception_entry:
	j exception_handler
	nop

exception_handler:
	KERNEL_STACK_TO_K0
	
	sub $k0, REGISTER_SPACE
	sw $sp, EOFFSET_SP($k0)
	move $sp, $k0
	
	mfc0 $k0, $cause
	
	sra $k0, $k0, 0x2    # cp0_exc_cause() part 1
	andi $k0, $k0, 0x1f  # cp0_exc_cause() part 2
	sub $k0, 8           # 8 = SYSCALL
	
	beqz $k0, syscall_shortcut
	add $k0, 8           # Revert $k0 back to correct exc number
	
	REGISTERS_STORE_AND_EXC_RESET $sp
	
	move $a1, $sp
	jal exc_dispatch     # exc_dispatch(excno, register_space)
	move $a0, $k0
	
	REGISTERS_LOAD $sp
	# The $sp is automatically restored to former value
	eret

## Syscall entry
#
# Registers:
#
# @param v0		Syscall number.
# @param a0		1st argument.
# @param a1		2nd argument.
# @param a2		3rd argument.
# @param a3		4th argument.
# @param t0		5th argument.
# @param t1		6th argument.
#
# @return		The return value will be stored in v0.
#
#define SS_SP		EOFFSET_SP
#define SS_STATUS	EOFFSET_STATUS
#define SS_EPC		EOFFSET_EPC
#define SS_K1		EOFFSET_K1
syscall_shortcut:
	# We have a lot of space on the stack, with free use
	mfc0 $t3, $epc
	mfc0 $t2, $status
	sw $t3, SS_EPC($sp)		# Save EPC
	sw $k1, SS_K1($sp)   		# Save k1 not saved on context switch
	
	and $t4, $t2, REG_SAVE_MASK	# Save only KSU, EXL, ERL, IE
	li $t5, ~(0x1f)
	and $t2, $t2, $t5		# Clear KSU, EXL, ERL
	ori $t2, $t2, 0x1		# Set IE

	sw $t4, SS_STATUS($sp)
	mtc0 $t2, $status

	#
	# Call the higher level system call handler
	# We are going to reuse part of the unused exception stack frame
	#
	sw $t0, STACK_ARG4($sp)		# save the 5th argument on the stack
	sw $t1, STACK_ARG5($sp)		# save the 6th argument on the stack
	jal syscall_handler
	sw $v0, STACK_ARG6($sp)		# save the syscall number on the stack

	# restore status
	mfc0 $t2, $status
	lw $t3, SS_STATUS($sp)

	# Change back to EXL = 1 (from last exception), otherwise
	# an interrupt could rewrite the CP0 - EPC
	li $t4, ~REG_SAVE_MASK		# Mask UM, EXL, ERL, IE
	and $t2, $t2, $t4
	or $t2, $t2, $t3		# Copy saved UM, EXL, ERL, IE
	mtc0 $t2, $status
			
	# restore epc + 4
	lw $t2, SS_EPC($sp)
	lw $k1, SS_K1($sp)
	addi $t2, $t2, 4
	mtc0 $t2, $epc
	
	lw $sp, SS_SP($sp)		# restore sp
	
	eret

tlb_refill_handler:
	KERNEL_STACK_TO_K0
	sub $k0, REGISTER_SPACE
	REGISTERS_STORE_AND_EXC_RESET $k0
	sw $sp,EOFFSET_SP($k0)
	add $sp, $k0, 0

	jal tlb_refill
	add $a0, $sp, 0 

	REGISTERS_LOAD $sp

	eret

cache_error_handler:
	KERNEL_STACK_TO_K0
	sub $k0, REGISTER_SPACE
	REGISTERS_STORE_AND_EXC_RESET $k0
	sw $sp,EOFFSET_SP($k0)
	add $sp, $k0, 0

	jal cache_error
	add $a0, $sp, 0 

	REGISTERS_LOAD $sp

	eret

userspace_asm:
	add $sp, $a0, 0
	add $v0, $a1, 0 
	add $t9, $a2, 0			# Set up correct entry into PIC code
	xor $a0, $a0, $a0		# $a0 is defined to hold pcb_ptr
					# set it to 0
	eret