/*
 * linux/arch/nios2/kernel/entry.S
 *
 * Copyright (C) 2013-2014  Altera Corporation
 * Copyright (C) 2009, Wind River Systems Inc
 *
 * Implemented by fredrik.markstrom@gmail.com and ivarholmqvist@gmail.com
 *
 *  Copyright (C) 1999-2002, Greg Ungerer (gerg@snapgear.com)
 *  Copyright (C) 1998  D. Jeff Dionne <jeff@lineo.ca>,
 *                      Kenneth Albanowski <kjahds@kjahds.com>,
 *  Copyright (C) 2000  Lineo Inc. (www.lineo.com)
 *  Copyright (C) 2004  Microtronix Datacom Ltd.
 *
 * 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.
 *
 * Linux/m68k support by Hamish Macdonald
 *
 * 68060 fixes by Jesper Skov
 * ColdFire support by Greg Ungerer (gerg@snapgear.com)
 * 5307 fixes by David W. Miller
 * linux 2.4 support David McCullough <davidm@snapgear.com>
 */

#include <linux/sys.h>
#include <linux/linkage.h>
#include <asm/asm-offsets.h>
#include <asm/asm-macros.h>
#include <asm/thread_info.h>
#include <asm/errno.h>
#include <asm/setup.h>
#include <asm/entry.h>
#include <asm/unistd.h>
#include <asm/processor.h>

.macro GET_THREAD_INFO reg
.if THREAD_SIZE & 0xffff0000
        andhi   \reg, sp, %hi(~(THREAD_SIZE-1))
.else
        addi    \reg, r0, %lo(~(THREAD_SIZE-1))
        and     \reg, \reg, sp
.endif
.endm

.macro  kuser_cmpxchg_check
        /*
         * Make sure our user space atomic helper is restarted if it was
         * interrupted in a critical region.
         * ea-4 = address of interrupted insn (ea must be preserved).
         * sp = saved regs.
         * cmpxchg_ldw = first critical insn, cmpxchg_stw = last critical insn.
         * If ea <= cmpxchg_stw and ea > cmpxchg_ldw then saved EA is set to
         * cmpxchg_ldw + 4.
        */
        /* et = cmpxchg_stw + 4 */
        movui   et, (KUSER_BASE + 4 + (cmpxchg_stw - __kuser_helper_start))
        bgtu    ea, et, 1f

        subi    et, et, (cmpxchg_stw - cmpxchg_ldw) /* et = cmpxchg_ldw + 4 */
        bltu    ea, et, 1f
        stw     et, PT_EA(sp)   /* fix up EA */
        mov     ea, et
1:
.endm

.section .rodata
.align 4
exception_table:
        .word unhandled_exception       /* 0 - Reset */
        .word unhandled_exception       /* 1 - Processor-only Reset */
        .word external_interrupt        /* 2 - Interrupt */
        .word handle_trap               /* 3 - Trap Instruction */

        .word instruction_trap          /* 4 - Unimplemented instruction */
        .word handle_illegal            /* 5 - Illegal instruction */
        .word handle_unaligned          /* 6 - Misaligned data access */
        .word handle_unaligned          /* 7 - Misaligned destination address */

        .word handle_diverror           /* 8 - Division error */
        .word protection_exception_ba   /* 9 - Supervisor-only instr. address */
        .word protection_exception_instr /* 10 - Supervisor only instruction */
        .word protection_exception_ba   /* 11 - Supervisor only data address */

        .word unhandled_exception       /* 12 - Double TLB miss (data) */
        .word protection_exception_pte  /* 13 - TLB permission violation (x) */
        .word protection_exception_pte  /* 14 - TLB permission violation (r) */
        .word protection_exception_pte  /* 15 - TLB permission violation (w) */

        .word unhandled_exception       /* 16 - MPU region violation */

trap_table:
        .word   handle_system_call      /* 0  */
        .word   handle_trap_1           /* 1  */
        .word   handle_trap_2           /* 2  */
        .word   handle_trap_3           /* 3  */
        .word   handle_trap_reserved    /* 4  */
        .word   handle_trap_reserved    /* 5  */
        .word   handle_trap_reserved    /* 6  */
        .word   handle_trap_reserved    /* 7  */
        .word   handle_trap_reserved    /* 8  */
        .word   handle_trap_reserved    /* 9  */
        .word   handle_trap_reserved    /* 10 */
        .word   handle_trap_reserved    /* 11 */
        .word   handle_trap_reserved    /* 12 */
        .word   handle_trap_reserved    /* 13 */
        .word   handle_trap_reserved    /* 14 */
        .word   handle_trap_reserved    /* 15 */
        .word   handle_trap_reserved    /* 16 */
        .word   handle_trap_reserved    /* 17 */
        .word   handle_trap_reserved    /* 18 */
        .word   handle_trap_reserved    /* 19 */
        .word   handle_trap_reserved    /* 20 */
        .word   handle_trap_reserved    /* 21 */
        .word   handle_trap_reserved    /* 22 */
        .word   handle_trap_reserved    /* 23 */
        .word   handle_trap_reserved    /* 24 */
        .word   handle_trap_reserved    /* 25 */
        .word   handle_trap_reserved    /* 26 */
        .word   handle_trap_reserved    /* 27 */
        .word   handle_trap_reserved    /* 28 */
        .word   handle_trap_reserved    /* 29 */
#ifdef CONFIG_KGDB
        .word   handle_kgdb_breakpoint  /* 30 KGDB breakpoint */
#else
        .word   instruction_trap                /* 30 */
#endif
        .word   handle_breakpoint       /* 31 */

.text
.set noat
.set nobreak

ENTRY(inthandler)
        SAVE_ALL

        kuser_cmpxchg_check

        /* Clear EH bit before we get a new excpetion in the kernel
         * and after we have saved it to the exception frame. This is done
         * whether it's trap, tlb-miss or interrupt. If we don't do this
         * estatus is not updated the next exception.
         */
        rdctl   r24, status
        movi    r9, %lo(~STATUS_EH)
        and     r24, r24, r9
        wrctl   status, r24

        /* Read cause and vector and branch to the associated handler */
        mov     r4, sp
        rdctl   r5, exception
        movia   r9, exception_table
        add     r24, r9, r5
        ldw     r24, 0(r24)
        jmp     r24


/***********************************************************************
 * Handle traps
 ***********************************************************************
 */
ENTRY(handle_trap)
        ldwio   r24, -4(ea)     /* instruction that caused the exception */
        srli    r24, r24, 4
        andi    r24, r24, 0x7c
        movia   r9,trap_table
        add     r24, r24, r9
        ldw     r24, 0(r24)
        jmp     r24


/***********************************************************************
 * Handle system calls
 ***********************************************************************
 */
ENTRY(handle_system_call)
        /* Enable interrupts */
        rdctl   r10, status
        ori     r10, r10, STATUS_PIE
        wrctl   status, r10

        /* Reload registers destroyed by common code. */
        ldw     r4, PT_R4(sp)
        ldw     r5, PT_R5(sp)

local_restart:
        stw     r2, PT_ORIG_R2(sp)
        /* Check that the requested system call is within limits */
        movui   r1, __NR_syscalls
        bgeu    r2, r1, ret_invsyscall
        slli    r1, r2, 2
        movhi   r11, %hiadj(sys_call_table)
        add     r1, r1, r11
        ldw     r1, %lo(sys_call_table)(r1)

        /* Check if we are being traced */
        GET_THREAD_INFO r11
        ldw     r11,TI_FLAGS(r11)
        BTBNZ   r11,r11,TIF_SYSCALL_TRACE,traced_system_call

        /* Execute the system call */
        callr   r1

        /* If the syscall returns a negative result:
         *   Set r7 to 1 to indicate error,
         *   Negate r2 to get a positive error code
         * If the syscall returns zero or a positive value:
         *   Set r7 to 0.
         * The sigreturn system calls will skip the code below by
         * adding to register ra. To avoid destroying registers
         */
translate_rc_and_ret:
        movi    r1, 0
        bge     r2, zero, 3f
        ldw     r1, PT_ORIG_R2(sp)
        addi    r1, r1, 1
        beq     r1, zero, 3f
        sub     r2, zero, r2
        movi    r1, 1
3:
        stw     r2, PT_R2(sp)
        stw     r1, PT_R7(sp)
end_translate_rc_and_ret:

ret_from_exception:
        ldw     r1, PT_ESTATUS(sp)
        /* if so, skip resched, signals */
        TSTBNZ  r1, r1, ESTATUS_EU, Luser_return

restore_all:
        rdctl   r10, status                     /* disable intrs */
        andi    r10, r10, %lo(~STATUS_PIE)
        wrctl   status, r10
        RESTORE_ALL
        eret

        /* If the syscall number was invalid return ENOSYS */
ret_invsyscall:
        movi    r2, -ENOSYS
        br      translate_rc_and_ret

        /* This implements the same as above, except it calls
         * do_syscall_trace_enter and do_syscall_trace_exit before and after the
         * syscall in order for utilities like strace and gdb to work.
         */
traced_system_call:
        SAVE_SWITCH_STACK
        call    do_syscall_trace_enter
        RESTORE_SWITCH_STACK

        /* Create system call register arguments. The 5th and 6th
           arguments on stack are already in place at the beginning
           of pt_regs. */
        ldw     r2, PT_R2(sp)
        ldw     r4, PT_R4(sp)
        ldw     r5, PT_R5(sp)
        ldw     r6, PT_R6(sp)
        ldw     r7, PT_R7(sp)

        /* Fetch the syscall function. */
        movui   r1, __NR_syscalls
        bgeu    r2, r1, traced_invsyscall
        slli    r1, r2, 2
        movhi   r11,%hiadj(sys_call_table)
        add     r1, r1, r11
        ldw     r1, %lo(sys_call_table)(r1)

        callr   r1

        /* If the syscall returns a negative result:
         *   Set r7 to 1 to indicate error,
         *   Negate r2 to get a positive error code
         * If the syscall returns zero or a positive value:
         *   Set r7 to 0.
         * The sigreturn system calls will skip the code below by
         * adding to register ra. To avoid destroying registers
         */
translate_rc_and_ret2:
        movi    r1, 0
        bge     r2, zero, 4f
        ldw     r1, PT_ORIG_R2(sp)
        addi    r1, r1, 1
        beq     r1, zero, 4f
        sub     r2, zero, r2
        movi    r1, 1
4:
        stw     r2, PT_R2(sp)
        stw     r1, PT_R7(sp)
end_translate_rc_and_ret2:
        SAVE_SWITCH_STACK
        call    do_syscall_trace_exit
        RESTORE_SWITCH_STACK
        br      ret_from_exception

        /* If the syscall number was invalid return ENOSYS */
traced_invsyscall:
        movi    r2, -ENOSYS
        br      translate_rc_and_ret2

Luser_return:
        GET_THREAD_INFO r11                     /* get thread_info pointer */
        ldw     r10, TI_FLAGS(r11)              /* get thread_info->flags */
        ANDI32  r11, r10, _TIF_WORK_MASK
        beq     r11, r0, restore_all            /* Nothing to do */
        BTBZ    r1, r10, TIF_NEED_RESCHED, Lsignal_return

        /* Reschedule work */
        call    schedule
        br      ret_from_exception

Lsignal_return:
        ANDI32  r1, r10, _TIF_SIGPENDING | _TIF_NOTIFY_RESUME
        beq     r1, r0, restore_all
        mov     r4, sp                  /* pt_regs */
        SAVE_SWITCH_STACK
        call    do_notify_resume
        beq     r2, r0, no_work_pending
        RESTORE_SWITCH_STACK
        /* prepare restart syscall here without leaving kernel */
        ldw     r2, PT_R2(sp)   /* reload syscall number in r2 */
        ldw     r4, PT_R4(sp)   /* reload syscall arguments r4-r9 */
        ldw     r5, PT_R5(sp)
        ldw     r6, PT_R6(sp)
        ldw     r7, PT_R7(sp)
        ldw     r8, PT_R8(sp)
        ldw     r9, PT_R9(sp)
        br      local_restart   /* restart syscall */

no_work_pending:
        RESTORE_SWITCH_STACK
        br      ret_from_exception

/***********************************************************************
 * Handle external interrupts.
 ***********************************************************************
 */
/*
 * This is the generic interrupt handler (for all hardware interrupt
 * sources). It figures out the vector number and calls the appropriate
 * interrupt service routine directly.
 */
external_interrupt:
        rdctl   r12, ipending
        rdctl   r9, ienable
        and     r12, r12, r9
        /* skip if no interrupt is pending */
        beq     r12, r0, ret_from_interrupt

        /*
         * Process an external hardware interrupt.
         */

        addi    ea, ea, -4      /* re-issue the interrupted instruction */
        stw     ea, PT_EA(sp)
2:      movi    r4, %lo(-1)     /* Start from bit position 0,
                                        highest priority */
                                /* This is the IRQ # for handler call */
1:      andi    r10, r12, 1     /* Isolate bit we are interested in */
        srli    r12, r12, 1     /* shift count is costly without hardware
                                        multiplier */
        addi    r4, r4, 1
        beq     r10, r0, 1b
        mov     r5, sp          /* Setup pt_regs pointer for handler call */
        call    do_IRQ
        rdctl   r12, ipending   /* check again if irq still pending */
        rdctl   r9, ienable     /* Isolate possible interrupts */
        and     r12, r12, r9
        bne     r12, r0, 2b
        /* br   ret_from_interrupt */ /* fall through to ret_from_interrupt */

ENTRY(ret_from_interrupt)
        ldw     r1, PT_ESTATUS(sp)      /* check if returning to kernel */
        TSTBNZ  r1, r1, ESTATUS_EU, Luser_return

#ifdef CONFIG_PREEMPTION
        GET_THREAD_INFO r1
        ldw     r4, TI_PREEMPT_COUNT(r1)
        bne     r4, r0, restore_all
        ldw     r4, TI_FLAGS(r1)                /* ? Need resched set */
        BTBZ    r10, r4, TIF_NEED_RESCHED, restore_all
        ldw     r4, PT_ESTATUS(sp)      /* ? Interrupts off */
        andi    r10, r4, ESTATUS_EPIE
        beq     r10, r0, restore_all
        call    preempt_schedule_irq
#endif
        br      restore_all

/***********************************************************************
 * A few syscall wrappers
 ***********************************************************************
 */
/*
 * int clone(unsigned long clone_flags, unsigned long newsp,
 *              int __user * parent_tidptr, int __user * child_tidptr,
 *              int tls_val)
 */
ENTRY(sys_clone)
        SAVE_SWITCH_STACK
        subi    sp, sp, 4 /* make space for tls pointer */
        stw     r8, 0(sp) /* pass tls pointer (r8) via stack (5th argument) */
        call    nios2_clone
        addi    sp, sp, 4
        RESTORE_SWITCH_STACK
        ret
/* long syscall(SYS_clone3, struct clone_args *cl_args, size_t size); */
ENTRY(__sys_clone3)
        SAVE_SWITCH_STACK
        call    sys_clone3
        RESTORE_SWITCH_STACK
        ret

ENTRY(sys_rt_sigreturn)
        SAVE_SWITCH_STACK
        mov     r4, sp
        call    do_rt_sigreturn
        RESTORE_SWITCH_STACK
        addi    ra, ra, (end_translate_rc_and_ret - translate_rc_and_ret)
        ret

/***********************************************************************
 * A few other wrappers and stubs
 ***********************************************************************
 */
protection_exception_pte:
        rdctl   r6, pteaddr
        slli    r6, r6, 10
        call    do_page_fault
        br      ret_from_exception

protection_exception_ba:
        rdctl   r6, badaddr
        call    do_page_fault
        br      ret_from_exception

protection_exception_instr:
        call    handle_supervisor_instr
        br      ret_from_exception

handle_breakpoint:
        call    breakpoint_c
        br      ret_from_exception

#ifdef CONFIG_NIOS2_ALIGNMENT_TRAP
handle_unaligned:
        SAVE_SWITCH_STACK
        call    handle_unaligned_c
        RESTORE_SWITCH_STACK
        br      ret_from_exception
#else
handle_unaligned:
        call    handle_unaligned_c
        br      ret_from_exception
#endif

handle_illegal:
        call    handle_illegal_c
        br      ret_from_exception

handle_diverror:
        call    handle_diverror_c
        br      ret_from_exception

#ifdef CONFIG_KGDB
handle_kgdb_breakpoint:
        call    kgdb_breakpoint_c
        br      ret_from_exception
#endif

handle_trap_1:
        call    handle_trap_1_c
        br      ret_from_exception

handle_trap_2:
        call    handle_trap_2_c
        br      ret_from_exception

handle_trap_3:
handle_trap_reserved:
        call    handle_trap_3_c
        br      ret_from_exception

/*
 * Beware - when entering resume, prev (the current task) is
 * in r4, next (the new task) is in r5, don't change these
 * registers.
 */
ENTRY(resume)

        rdctl   r7, status                      /* save thread status reg */
        stw     r7, TASK_THREAD + THREAD_KPSR(r4)

        andi    r7, r7, %lo(~STATUS_PIE)        /* disable interrupts */
        wrctl   status, r7

        SAVE_SWITCH_STACK
        stw     sp, TASK_THREAD + THREAD_KSP(r4)/* save kernel stack pointer */
        ldw     sp, TASK_THREAD + THREAD_KSP(r5)/* restore new thread stack */
        movia   r24, _current_thread            /* save thread */
        GET_THREAD_INFO r1
        stw     r1, 0(r24)
        RESTORE_SWITCH_STACK

        ldw     r7, TASK_THREAD + THREAD_KPSR(r5)/* restore thread status reg */
        wrctl   status, r7
        ret

ENTRY(ret_from_fork)
        call    schedule_tail
        br      ret_from_exception

ENTRY(ret_from_kernel_thread)
        call    schedule_tail
        mov     r4,r17  /* arg */
        callr   r16     /* function */
        br      ret_from_exception

/*
 * Kernel user helpers.
 *
 * Each segment is 64-byte aligned and will be mapped to the <User space>.
 * New segments (if ever needed) must be added after the existing ones.
 * This mechanism should be used only for things that are really small and
 * justified, and not be abused freely.
 *
 */

 /* Filling pads with undefined instructions. */
.macro  kuser_pad sym size
        .if     ((. - \sym) & 3)
        .rept   (4 - (. - \sym) & 3)
        .byte   0
        .endr
        .endif
        .rept   ((\size - (. - \sym)) / 4)
        .word   0xdeadbeef
        .endr
.endm

        .align  6
        .globl  __kuser_helper_start
__kuser_helper_start:

__kuser_helper_version:                         /* @ 0x1000 */
        .word   ((__kuser_helper_end - __kuser_helper_start) >> 6)

__kuser_cmpxchg:                                /* @ 0x1004 */
        /*
         * r4 pointer to exchange variable
         * r5 old value
         * r6 new value
         */
cmpxchg_ldw:
        ldw     r2, 0(r4)                       /* load current value */
        sub     r2, r2, r5                      /* compare with old value */
        bne     r2, zero, cmpxchg_ret

        /* We had a match, store the new value */
cmpxchg_stw:
        stw     r6, 0(r4)
cmpxchg_ret:
        ret

        kuser_pad __kuser_cmpxchg, 64

        .globl  __kuser_sigtramp
__kuser_sigtramp:
        movi    r2, __NR_rt_sigreturn
        trap

        kuser_pad __kuser_sigtramp, 64

        .globl  __kuser_helper_end
__kuser_helper_end: